The Cactus bonus round rule is one of the many rules that can be applied during the Bonus Round episodes. It has a chance to spawn on floors 2 and 3 for every character, but is more likely on floor 2.

Cactus

When you defeat an enemy, excessive damage is reflected back at you.

When the rule activates, the Reflect status is added to all enemies. Damage dealt that exceeds the enemy's HP will be reflected back at the player, making it so that precise fighting is necessary. For example, if you use a Battle Axe to deal 8 damage to an enemy with 5 health left, you will defeat the enemy but take (8-5) = 3 damage. The effect also extends to Poison damage: if you inflict 5 Poison on an enemy with 2 health, you will take 3 damage once the enemy is defeated.

This rule can make things harder if the Kraken bonus round rule is in place, since you won't be able to see the enemy's health.

The damage reflected will never be fatal: if you defeat the enemy you will always survive with 1 health.