Vile Spider

Arach, the Vile Spider was a boss that has since been removed from the game.

Boss Room
Arach's boss room is a simple rectangular room with some platforms for the player to stand on.

Force Nova
Arach emits a Force Nova, damaging any players around the mech. This move also spawns several Creeps depending on the level of the boss.

Walking
Arach will walk somewhere random on the platform he's currently standing on, with the intent of dealing contact damage with the player.

Jumping
Arach will jump onto a wall, or back onto the floor if he's already standing on a wall.

Weakness
Arach is weak to Mortar. Hitting Arach with Mortar does nothing special other than the double damage, however.