Use the red-eye warning
Malevolence shows red eyes, applies Charged and gives Slasher level 10 DEF Up for two turns. The charged attack is Jump Stab: a high leap into a 25-damage piercing strike. It is not the ordinary Cleave that follows Malevolence in the normal-move list.
Choose the avoidance action before the leap
Ghost Potion makes its user Invisible for a turn and then Exhausted. Use it before the charged strike, not after the damage lands. Keep HP high enough to handle the action you lose afterward. Unlike Azure Blast, Jump Stab is not listed as an unguardable attack; this potion route trades an action for avoiding its difficult timing.
Mechanics references: Ghost Potion
Other moves
Slasher Signature attacks from several angles four times for 2 piercing damage each. Cleave is an immediate close-range strike for 5 and can Silence for two turns. Watch the status before assuming an SP heal is available. Slasher has 30 base HP and guards the Catacombs entrance.