Echo

Location
It is automatically acquired once Felix’s party leaves Daila and enters the overworld for the first time, where a cutscene has Echo talking to him and give a tutorial on how to use Djinn. It is nearly identical to Venus Djinni Flint from the first game in its speaking role as the "tutorial Djinni" of its respective game. It will join you no matter how many times you attempt to refuse it joining you, but its various amusing responses range from outright begging to promising that Felix will be “all kinds of strong” and that Echo “won’t be a burden and eat all your chips or anything”.

Description
When Set, it increases base HP by 9, base PP by 4, and base Attack by 3.

When Echo's battle effect is used, the user attacks a target with a two-hit strike that propels the target into the air, dealing a Venus-based attack equal in power to the user's normal physical attack increased by 60%. This effect is identical to the battle ability of Flint in Golden Sun.

Ability analysis
From when Echo is first acquired all the way up until Isaac's party joins Felix's late in The Lost Age, Echo is the premier damaging Venus Djinni, sporting a damage multiplier higher than any Djinn of any other element. It will likely be used throughout the game more than the other attacking Djinn you can get, which are Steel with its +30% modifier and its health-leeching property and Meld with its somewhat gimmicky mechanic involving a modifier that is even lower. As soon as Isaac joins and brings the identical Flint along with him, though, they both will immediately be obsoleted by a Djinni easily found in Atteka Inlet, Geode, which has a consistent damage multiplier of +90%.

Name Origin
Echoes are notorious in cave systems. Caves are made out of rock. Venus Djinn are based on rock.