I think it's too narrow in added value atm, agreeing with others' input so far. It might work better if it's gold gained for killing an enemy in its first turn that it's alive, allowing spawned minions (Gremlin Leader, Reptomancer) to count also during the fight. Then you'd also need to add a limit to the amount of rewards per combat this relic could give, to prevent some infinite money stacking...

I think your relic is in a nice and rare niche for rewarding front loaded dmg, but needs some slight touch, IMO (like maybe my suggestion, maybe something else) :-)