Mad Beast is Jill Valentine's Level 3 Hyper Combo.
Jill enters a permanent state of Feral Crouch until the meter runs out, and she is left unable to guard high, or move around normally. Inputting any direction will cause her to quickly teleport in that direction. She is able to teleport in any direction, as well is in the air.
Also See[]
Jill Valentine's moves in Marvel vs. Capcom 3: Fate of Two Worlds