Well, slightly different for a sealstone effect idea... Maybe.
Focused Power Sealstone - X: Field effect. Choose either Physical or Magic. Replace X with the chosen type. Damage from attacks, probabilities and healing of the chosen type are raised by 20%, while damage from attacks, probabilities, and healing of the type not chosen are lowered by 20%. Damage from attacks, probabilities, and healing that is non-typed is considered the type not chosen for calculation of effects. After choosing the initial effect, it CANNOT be changed between floors.
It's a stone that punishes having (for example) Deis and Emily on a team, since one of them is having their overall effect reduced (unless you're only using Deis for her buffs! But that's neither here nor there). Chemists having the effects of their items reduced is hard on them too, but if Kuja's anywhere in the dungeon, he hates having his Flare Star reduced too (unless it's blocked by either Protect or Shell. I'm not sure if it is).