How to Play Undertale Red

1. The three routes

Just like the main game, Undertale Red has three different routes: Pacifist, Neutral, and Genocide. You need to do different things to go down each route.

Pacifist Route:

You need to not attack Red at all. You first have to talk with Red three times (or just once if this isn't your first playthrough). She'll quickly become upset that you don't fight back. Note that if you use joke instead of talk, she'll get annoyed and just leave, leading to a reset.

This, unfortunately, angers her and she will add to her attack moveset significantly. However, you just need to survive and keep striking up a conversation with her, and eventually she will let her guard down and let you MERCY her. 

Do note that after the mercy option is available, you can betray her and FIGHT her, killing her instantly. This is technically an ending, but is tied to the pacifist route.

Neutral Route:

You'll need to defend yourself until Red decides that you were fighting back in self-defence and she offers to let you go. You can now select the Save option, and if you do that, you will have achieved the neutral route and the game will end.

Genocide Route:

This is the same as the Neutral Route, except instead of saving her, you attack her when she offers to let you go.

This will make her go all out and spawn two royal guards to fight with her. These guardians have a variety of different attacks and will turn the fight into a flat out bullet hell.

2. Red's Moveset

Here is her moveset in the Pacifist and Neutral Routes:

• Red battles her sword and causes a certain line harm (horizontal, vertical, horizontal). Make sure to stay away from the direction she's cutting.
• Red swings her sabers (vertical and horizontal, or two diagonals). Again, stay away from the telegraphed swing locations.
• Red can split the battlefield into many parts by using other attacks. Make sure to stay away from them and keep in mind that you'll be stuck in the section you picked.
• On the battlefield, there are one or more bombs after which the Red divides in many sections. The bomb can only cause damage in their section. Make sure to manuever in a way that will end up with the bombs in a section away from you.
• Lines cut through the box on the battlefield, and then Red slashes every thread. Don't get overwhelmed.  There's always a pattern, and you can pretty easily find a safe spot to hide.
• Splits the battlefield and Red summons gears. Just stay away from the gears, it's not too difficult.

And now here are her genocide moves. Or more accurately, here are the Royal Guardian's moves, because she barely does anything herself. All she does is split the battlefield.

• Orange attack — lasers coming from the Delta Runes, rotating around them. The rotation speed increases over time.
• Blue Attack – Expanding circle appears with circular runes.
• Purple Attack – Wide spheres of purple energy are shot off by runes.
• 

She will start spamming all of these attacks at you at once during a certain genocide gauntlet. Fun fact, you will get different dialogue depending on how much damage you took! It doesn't actually matter, but it's a very fun touch.

And that's pretty much it. If you keep all of these attacks in mind and prepare yourself mentally while also paying attention to all the patterns that are inherent to Red's attacks, then you're more than ready to beat her.