Divine Retribution
Conquistador de pan
I'm thinking of a two stage fast attacker with a new ability that gives it priority when using a physical move of one of it's types. (So in normal conditions physical Ground and Electric moves would get priority but if it was it hit by soak (for example) then physical water type moves would get priority instead)
Talonflame proved that having priority on just one type can be terrifying, even with a mediocre attack stat. Having priority on both STABs (especially with a type combo as solid as Ground/Electric) would be even worse. If such an ability were to ever exist, it would need a pretty severe drawback to balance it (like the fact that Gale Wings only works when the user is at full HP in Gen 7).