Kind of mixes with the token/swarm thing pretty badly I think. Could also easily cause massive life loss for 2 mana in general.

Interesting interaction with Unbound.

I don't find this very interesting, honestly. It feels like a bland hate card. I'd rather have something more general.

I'd prefer something like "Permanents your opponent control can't untap outside of their controller's untap step unless their controller pays 1 life".

DJK's idea is more directed towards opponents.

In both cases, one concern is that the idea here is narrow in that it's only anti-unbound. In most cases it would be useless outside the set, and within the set it mostly only applies to unbound creatures.

We could do a rare idea along the lines of "Creatures don't untap during their controller's untap step unless that player pays 1/2 life" might be doable as enchantment. It also would be exploitable if you do use Unbound, as it matters a bit less.

The idea of untap step based stuff is an area we could experiment with in its interaction with unbound. As well as more ability type stuff.