This needs to be an Aura, right?
It could be an aura, but then it's vulnerable to both creature removal and enchantment removal.It doesn't need to be an aura because players will exile the target under their creature just as they would with Banisher Priest. That does add the tiniest bit of memory, but it shouldn't be significant.
It'd be a good Selesnya design also.
You like the "Power less than power of [creature you control]" clause a lot, but it always reads as super mathy to me. My Proposal:Detain for Questioning 1WEnchantmentWhen ~ ETBs, exile target creature for as long as you control two or more creatures.
The wording of this is insanely weird, because it's an enchantment but once it ETBs it stops doing anything (as worded, the effect is totally separate -- that is, it's not linked to whether the enchantment remains on the field or not)
I could see doing this as a sorcery in a set with an "as long as you control two or more creatures" ability word, so that it's a condition people are set up to be tracking anyway, rather than a one-off thing to remember.
Agree, I didn't think of that. I'd probably say Exile it for as long as ~ remains in play. When you control fewer than two creatures, sacrifice ~. ---That way it meets the desired property of working correctly with enchantment removal!