Final Gaster is a boss located behind a fake wall in underfell snowdin, you will need the scythe, error blaster and max level to battle Final Gaster.
Phase 1 Attack’s:
Green hand: Traps a player in a bubble, can be popped by scythe.
Yellow hand: Fires a mini projectile, deals damage.
Orange hand: Spawns explosions randomly and deals high damage.
Purple hand: Summons a bone zone, if Final Gaster is at half health, he will use a void that will suck players that get in it and do devastating damage.
Teal hand: Traps a player in a string.
Blue hand: Summons a mini saw that deals devastating damage.
Red hand: Fire a octo blaster like Betty.
When Final Gaster gets to zero health, Phase 2 will begin, in phase 2 Final Gaster will become a blaster with hands.
Gaster’s Blaster: Fires a huge blaster beam where a player is standing.
Hands: Throws a hand at a player, instant kills.
Ring: A hand will randomly summon a ring, if there is lag the ring will simply fall.
Floor flip: will flip the floor, if it’s laggy then the flip will just go on its side and go back to normal.
Bones: Summons bones on the floor randomly like Nightmare Sans in Survive The Monsters.
Void: Will suck players into a ball, though it can be denied by using scythe.
After you beat final gaster you go to a button screen, either you MERCY or FIGHT, if you mercy error sans will kidnap Final gaster and you’ll get the gaster hand.