regigas ability is bad but can be negated with alolan muk, so the question becomes is that attack strong enough to justify attaching 5 energy to and can we attach it quickly enough before its KOed.
well we can attach 1 energy and 2 DCE to it, not ideal but doable, can use magnezone or vikavolt for the quick attach, can use shining legends venusaur to double grass so we only need 3 grass attached, can use metagross gx to attach metal/psychic from discard. finally we have yveltal, rayquaza and shining legends raikou that can attach from discard as part of an attack.
so there's options but is 160 (190 with choice) and stadium discard worth it, I say maybe we'll need to see what the other regis are, and frankly i'm leaning towards magnezone/vikavolt combined with raikou or rayquaza.