Tattermunge Duo

Whenever you cast a red spell, Tattermunge Duo gets +1/+1 until end of turn.
Whenever you cast a green spell, Tattermunge Duo gains forestwalk until end of turn. (It can't be blocked as long as defending player controls a Forest.)

Possessed Aven

Flying
Threshold — As long as seven or more cards are in your graveyard, Possessed Aven gets +1/+1, is black, and has "{2}{B}, {T}: Destroy target blue creature."

Sharktocrab

{2}{G}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Sharktocrab, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Coiling Oracle

When Coiling Oracle enters, reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put that card into your hand.