Vengeful Spirit

Vengeful Spirit (VS) allows you to shoot fireballs in order to quickly kill enemies or to cross larger gaps by taking advantage of the knock-back. Fireballs can be pogoed, allowing for a precise trick known as slopeball.

Greenpath
These skips make use of the knock-back when shooting a fireball. Jump as late as possible, tap right, cast VS but do not spam, hold left. Press QUICK CAST rather than FOCUS/CAST. For controller, fireb0rn recommends to swap QUICK CAST and DREAM NAIL so that you can cast VS with your thumb.

If you fail the Fireball Skip in the room where you see Hornet the first time, you can pogo off a Squit to back it up.

Queen's Station
By shooting three fireballs, it is barely possible to enter Fungal Wastes from Queen's Station without the Dash ability. This skip is used in Low% NMG.

Double hits
By shooting in the direction an enemy is moving, you can hit it twice with one fireball.