Sap

Location
It is found in Vault; first, ring the bell to make Sap hop to the cave exit, then traverse and complete Vault Cave where you will be able to reach Sap as your reward.

Description
When Set, it increases base HP by 10, base Attack by 3, and base Luck by 1.

When used, Sap damages the foe with Venus damage 50 points above the user’s base normal attack damage and adds 50% of the damage done to the user’s HP.

Analysis
While Sap certainly isn't the strongest attacking Djinni, it is one of the few Venus Djinn that actually does damage, and the draining side effect is always useful, especially in the Colosseum where Isaac is flying solo.

Name Origin
Sap is a liquid substance, usually sticky, that is found in many trees. Take note that not all liquids within trees are considered sap. "Sap" is also a verb, meaning "to drain."