Sap

Location
Sap is present in the town of Vault, but the requirement to attain it is quite involved and easy to unknowingly make mistakes about. First, in the town area, climb and make your way all the way to the wooden watch tower at the north end of the town, and interact with the dangling bell next to the NPC; a hollow ringing noise will prompt Sap to hop out of its hiding place in the nearby tree to an elevated area next to a cave exit. Then, go to the cemetery where the dog is, cast Reveal, climb down the revealed ladder, and complete the Vault Cave optional dungeon. At the end of the dungeon, you will exit out into the open out of said cave exit, and Sap will be sitting nearby in the spot you hounded it to, ready to be collected. In other words, Sap is the "end reward" of the Vault Cave dungeon, but only if you remember to place it as the dungeon's end reward first.

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

When Sap's battle effect is used, the user strikes the target and siphons a glowing yellow energy out of it, dealing a Venus-based attack equal in power to the user's normal physical attack with an additional 50 damage points added to the result. There is then a chance that the user's HP will be restored by an amount equal to 50% of the damage dealt to the target. This is similar to the TLA Venus Djinni, Steel, but the bonus damage of that Djinni is determined by a 1.3x damage multiplier.

Ability analysis
Since Flint from the beginning of Golden Sun is the one attack Venus Djinni an Adept would need for the sake of dealing optimized damage, Sap and its added damage would then only be used for the sake of its potential additional self-healing effect. It can be situationally useful for cases where your Adept would be helped out by a chance to be healed somewhat, but it is not a staple. The Venus Djinni Bane, for comparison's sake, has a little more added damage and the chance to inflict the extremely useful Venom condition.

In The Lost Age, when Isaac's party joins Felix's party along with their returning Djinn, Sap's ability makes it a variation on Steel, a Venus Djinni acquired relatively early in the game in the Gabomba Statue, at a point where the party in that game is at around the same level as when the first game's party can be when they first acquire Sap. Steel, in comparison to the Flint-like Echo, is less used even when it is first acquired because of the same relationship between them as between Sap and Flint above, and at the endgame their shared effect is unspectacular compared to certain other attack Djinn such as Geode.

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."