Hotland

- After crossing a bridge from Waterfall you’ll wind up in hotty hotty Hotland. There’s a water cooler on the next screen; you can, if you wish, systematically drain the thing by dumping water onto the ground. It takes a while, though, and there’s seemingly no point... unless you got Undyne to chase you here. If so, you can dump water on her to revive her. This will allow you to head back to Waterfall, and, along with Papyrus, get to know Undyne at her house.

- To the east is a save point, as well as two guards who block you from heading north. South of here is a boat wrangler; he will shuttle you off to either Snowdin or the Waterfall, if you feel like travelling. While you’re on the boat he can provide you with tips to secrets spread throughout the game. To the east is a laboratory, which is your next destination.

- Head east through the darkened Lab. You’ll quickly run into Dr. Alphys, mentioned several times but not seen until now, and she’ll tell you about a horrifying human-killing robot named Mettaton. Uh oh. The aforementioned robot then shows up, and you’ll face a deadly quiz show that damages you every time you answer incorrectly - though as far as I can tell it’s impossible to lose. (You can also look at Alphys for the answers.) Once Mettaton leaves Alphys will upgrade your phone, allowing you to access Dimensional Boxes and get at your stuff much more easily. Ooo. While you're here, raid Alphys' fridge for Instant Noodles. (You can also look upstairs, but there’s not much to see.)

- Head out of the Lab through the eastern exit. In the next few areas the random battles will start up again, featuring the following foes:
  • Vulkins. These well-meaning volcano dudes will pelt you with fireballs from the sides, easy to dodge if you remain in the middle, and chains of lightning bolts which are more easily avoided if you remain near the corners of the box. Criticize the Vulkin to stop it from attacking, then Hug it, then go for the Spare.
  • Tsunderplanes. Wig-wearing, proud creatures with a secret love of humans, Tsunderplanes attack by sending jets into your box vertically and launching fireballs horizontally. Not too bad to dodge. They can also launch bombs from above, but these don’t show up until later in the fight. Tsunderplanes must first be Approached several times; doing this will cause the silhouettes of the planes in the box to appear as green. Touch these auras until the Tsunderplane is shy. Then you can Flirt with it, and, after, Spare the Tsunderplane. Huh.
  • Pyropes. Yep, it’s a rope with fire on top. Pyropes like to send ropes with fire betwixt ‘em your way; weave into the flames to avoid damage. They’ll also lob bombs, which you can avoid just by getting on the opposite side of the box. Pyropes can be satisfied by Heating Up twice, then Sparing ‘em.
- After a lengthy northbound walk of little note you’ll find a save point. This next area is filled with hopping platforms; the exit is in the northwest. If you take the southern hopping platform you’ll wind up in a small side area where you can grab a Burnt Pan on your left, so long as you time your hopping properly.

- There’s a line of lasers in the next area, and Alphys will give you a stumbling rundown on how they work: you need to walk through the orange lasers and stand still when the blue ones pass by. Simple enough. There’s a button at the end that deactivates them all.

- Next up is an intersection with a spinny hopping tile. Alphys will tell you to go right; heed her advice. The puzzle in the next area is easy enough - just slide the two boxes so one is in the middle of the puzzle and the other is on the right or the left. This will allow you to fire through one box and hit the other on the far side.

- Head to the left side of the intersection. Now you can access the second puzzle, which is similar to the first but trickier. Press up, left, down, and left again to create a path through. Now the door to the north of the intersection will open.

- Beyond is a pack of shenanigans, and wrapped inside them is a mini game where you have to avoid Mettaton’s flying ingredients. Nothing too difficult, so long as you try to keep yourself from lingering under Mettaton too often.

Blue lasers in Hotland. Stand still.
- There’s a save point ahead, and past that an elevator. The elevator’s a bit strange, as it can take you to four different destinations - but not all of them are immediately visible. You’ll need to move to different floors to even get the option to see some of them. They’re as follows:
  • R1: Entrance
  • R2: Next destination
  • L1: Takes you back to the intersection outside the Lab, near the beginning of Hotland
  • L2: Not yet accessible
- Hop off at R2 and head west. Assuming Papyrus is still alive, you can purchase Hot Dogs from Sans at the next stand. (If you ask Sans for more even after you run out of space in your inventory he'll start stacking them on your head. What a guy.) There’s a side path a short ways through the next area; head south and you can find a Stained Apron. Continue west to find a rather abortive little puzzle. Shrug. If you go directly north at the crossroads leading to the Apron you can find a hidden path leading to a secret area, where you can run across an optional boss. He will only appear here on October 10th at 8 pm. (Feel free to change your computer's internal clock.)

So Sorry

Though he's a boss, So Sorry is no big deal. Being an artist, So Sorry spends most of the battle drawing. More often than not he'll swing his tail, and it will change to orange (move to avoid damage) or blue (stay still) with each swing. He can also hurl large wads of paper at you, which aren't much more difficult to avoid, and after a while he'll create Doodlebogs to join the fight. Draw to send them away. After enough rounds the battle will more or less end successfully. You don't really get anything for it, but... yeah. So Sorry, everybody!

- The next area contains a large number of hoppy tiles on isolated platforms. Every time you hop you’ll hit a button that will flip the configuration of the buttons, so, uh, yay? Good times. Hop in the following directions to reach the exit, without hitting the first button:
  • Left
  • Down
  • Down
  • Up
  • Down
  • Left
  • Up
  • Up
  • Left
- There’s a save point to the west of the puzzle (mices!). Use it, ‘cause a miniboss battle is coming up.

The Royal Guards. Yes, Papyrus wants to be one of these guys.
Royal Guards

Nothing too bad. The Royal Guards utilize a vertical attack box, forcing you to weave between their strikes. Don’t move a hell of a lot and this isn’t difficult. Though the two Royal Guards are identical attack-wise, you need to deal with them differently. Start by Cleaning RG 02. This will cause green pieces of armour to fall during the next attack; touch enough of them and RG 02’s armour will come off, flustering RG 01 and making his attacks wiggle. Whisper to RG 01 to get a tender confession, then Spare to end the fight.

- After bypassing the Guards you’ll wind up on Mettaton’s TV show, and he’ll order you to report something interesting. Pick one of the items nearby, however, and you’ll discover that they’re all bombs. You need to engage them in battle and defuse each one within two minutes, before they explode. Move in counterclockwise fashion from the centre until you get them all. You need to Defuse from the Act menu, and make sure you Defuse once they’re inside the green box, ‘cause you’ll waste time otherwise.

- The exit to the east eventually leads you to elevator floor L2, which you can now take to L3. To the east you’ll find a Spider Bakery that sells items for ridiculous amounts. Past here is another room with lots of hoppy panels that lead to puzzles in the north and the south, and you need to complete both to continue east. Both are the same shooters as before. The northern puzzle can be solved by hitting left and right, and the southern puzzle can be solved by hitting left three times, up once, left twice, and right.

- There’s a save point through the exit to the east, and beyond that a whoooole lotta spider webs. Boss fight!

Muffet. She was a stretch goal!
Muffet

Tricksy battle. Muffet will immediately force you onto a series of horizontal threads when the battle begins, and you need to hop from thread to thread to avoid the spiders that clamber along ‘em. This gets harder and harder as you go along, because not only do the spiders get faster and more numerous, they’re joined by bouncing balls and boomerang-ish things. After a number of rounds Muffet will also sic her ‘pet’ on you, and you’ll have to flee upwards while avoiding more spiders. It’s a simple enough dodging game, with no real tricks to it - though if you want to lower the amount of damage you take, you can more or less bribe Muffet to lower her damage. The more you bribe her, the more it costs each time. 

The battle ends when you kill Muffet or you survive enough rounds, which will take a while. You can also end it by using one of the Spider items which you may still have after visiting the Ruins and the spidery bake sales there.

- Mettaton is disturbing. Shenanigans and a fight! Though it’s honestly quite easy, so let’s skip it, right? Right.

- Eventually you’ll wind up at a crossroads where the Nice Cream Vendor is having a going-out-of-business sale. Poor guy. You can buy Nice Cream here, but only if you're on the Neutral path. (If you spared the Royal Guards on Pacifist they'll have taken all of the ice cream, and the dude flat out isn't here on Genocide.) To the vendor's left is the path back to the rest of Hotland; to his right is the R3 elevator, which will return you to the entrance; up north is the MT Resort.

- On the right side of the MT Resort is a back alley with a special pair of vendors called Bratty and Catty. They have a few good items, but the main one you should buy is the Mystery Key, if you’re interested in plot stuff. It will open the home next to Napstablook’s in Waterfall, inside which you’ll find a ton of diary entries. To the left of the entrance, assuming Papyrus is alive, you'll find Sans; he wants to have dinner. Accommodate him.

- You can stay at the hotel for 200 gold, if you wish, and like the Inn of Snowdin it will temporarily grant you 10 extra HP - though you won't get your money back after your odd little snooze.

- In the hotel’s lobby you’ll find plenty of NPCs with whom to chat, including a save point. There’s a restaurant to your left and a line of rooms to your right; the last room in this line will duplicate your Dog Residues as much as you like, assuming you completed the piano side quest in Waterfall. (Not that you need the help.) This room will also change Hot Dogs...? into Hush Puppies, which are much better healing items, and can be sold at a substantial profit in the Temmie Village. The other two rooms here want Sea Tea, from Waterfall, and a Cinnamon Bun, from Snowdin; you'll receive 99 gold apiece.

- Back in the lobby you can find a burger shop in the northeast, including a vendor who has lots to say if you buy something. His items are expensive, but using them in an upcoming boss battle will make it a fair bit quicker. And to the north…

Core

- The elevator inside the Core isn’t working, and there’s a dead end to the right, so head left. Monsters start to appear in here:
  • Madjicks. These wily dudes will hurl crosses at you. Not too deadly, but they get bad if you choose the wrong Actions and get confused. Stare at both of the Madjick’s orbs, one at a time, to convince the beast that you’re a wizard. Spare follows.
  • Knight Knights. Mighty, armoured warriors, Knight Knights will send out massive spreads of bullets, but so long as you only focus on the immediate area around you the bullets aren’t that difficult to avoid. Sing to the Knight Knight until it’s asleep to get your Spare.
  • Whimsalots. They like butterflies. Not too difficult, though tricky in conjunction with other enemies. Console and Pray to get a Spare. After Consoling, some of Whimsalot’s attacks will heal instead.
  • Final Froggits. Advanced versions of Froggits; they also like to jump and spew flies, but in a more dangerous manner. Still, meh. Mystify and Spare.
  • Antistigmatisms. These horrid bullies hurl circular obstacles in your way, but aren’t a huge deal unless they’re attacking with other enemies. Don’t Pick On, then Pick On, to get the Spare option.
This area’s straightforward, but it’s wise to not listen to Alphys. Her instructions are pretty much always wrong, up until you hit the dense grid of blue lasers. Move, stop, move, stop. Eventually you’ll reach a save point at a crossroads; from this point on the Core becomes a maze. Here are some items of interest, from the crossroads:
  • If you go east one screen and two north you’ll find a trash can containing 100 gold.
  • Go one screen west, one north, and one more west to find a puzzle. Yep, the usual. Move the blocks into the side niches until there’s only one left in the middle to finish it up. If you complete the puzzle you’ll unlock a path to the east.
  • Continue north at the intersection from the puzzle and you’ll find a trash can containing a Glamburger.
  • Go north until you find a bridge. Here you can fight three battles to reach a switch that will also open the path in the east. You don’t need to do this and the puzzle. (Though if you want experience…)
Once you’ve completed one of these two tasks, go north and east. Across one last bridge you’ll find an elevator back to the entrance of Core, a save point, and the end of the road. Ooo, plot twists. Don’t go through here if you want to explore the world, ‘cause this is a point of no return. If you do go through, I suggest having several healing items in your Box which you can access via your Cell Phone. You may need them coming up, and there’s no way to get healing items otherwise.

Mettaton EX is coming out to play. Oh yeah, bay-bee.
Mettaton

This fight starts out fairly standard for Mettaton, and all you need to do is survive a few rounds. Mettaton uses projectile attacks; dodge around them. Fairly simple. Eventually you’ll get a prompt…

… and, once you flip his switch, Mettaton turns to Mettaton EX. This is where the fight heats up. Mettaton EX, the fabulous creature he is, has a slew of attacks:
  • He’ll send giant legs down towards you. Shoot them to make them move out of the way.
  • He’ll drop small versions of his boxy form towards you. Blow them up, as they’ll launch hearts at you en masse if they get too far down the screen.
  • He'll pull out a disco ball that sweeps lasers across you. The starting lasers will be blue, but they'll start turning white as the ball rotates. Shoot the ball to change the colour of the lasers to blue whenever you're about to get hit by a white one. So long as you don't move a muscle, you should be perfectly safe.
  • He’ll drop lines of boxes and bombs at you. Shoot the boxes and weave around the bombs. If you do attack the bombs, be sure to move out of their vertical blast radius immediately. Sometimes he’ll reverse these lines and bring them back up at you, so be ready to dodge from the bottom-up.
  • He’ll release the heart on his belt and use it to spew projectiles down at you. Stay low and fire upward at the heart to end the attack.
This fight is different from most in that you’re ‘damaging’ Mettaton EX by gaining ratings. (Only if you want to Spare him, mind. If you want him to die, smack his block right off. He makes weird noises.) The higher the ratings, the closer you are to the end of the fight. You’ll gain ratings by dishing out and taking damage, eating branded items (anything from the MTT Resort's hamburger joint), and performing pleasing Acts (I found Pose to be the consistently best, especially if you Pose when you’re badly injured and should be healing). Choose quickly, as your ratings will drop between battle sequences. Get your ratings up to 10,000, then survive one last heart-shooting sequence to end the battle.

(Fun fact: You need to write an 'essay' partway through the fight. Type gibberish and you'll get a few points. Type 'legs' anywhere in the gibberish and you'll get a nice boost, 'cause that's the 'right answer'. Type swear words and you'll lose points instead. It's a daytime TV show, remember? No cussing!)