Barrenton Cragtreads

Barrenton Cragtreads can't be blocked by red creatures.

Augur il-Vec

Shadow (This creature can block or be blocked by only creatures with shadow.)
Sacrifice Augur il-Vec: You gain 4 life. Activate only during your upkeep.

Assault Griffin

Aven Liberator

Flying
Morph {3}{W} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Aven Liberator is turned face up, target creature you control gains protection from the color of your choice until end of turn.

Aven Cloudchaser

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Aven Cloudchaser enters the battlefield, destroy target enchantment.