Insidious Mist

Hexproof, indestructible
Insidious Mist can't block and can't be blocked.
Whenever Insidious Mist attacks and isn't blocked, you may pay {2}{B}. If you do, transform it.

Elusive Tormentor

{1}, Discard a card: Transform Elusive Tormentor.

Elusive Tormentor // Insidious Mist

Blight Mamba

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{1}{G}: Regenerate Blight Mamba.

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Cephalid Constable

Whenever Cephalid Constable deals combat damage to a player, return up to that many target permanents that player controls to their owner's hand.