Kill a gnarlid with your first blow, or it'll cheerfully show you how it's done.

Aura Gnarlid

Creatures with power less than this creature's power can't block it.
This creature gets +1/+1 for each Aura on the battlefield.

Wilds of Eldraine Commander

Creatures with power less than Aura Gnarlid's power can't block it.
Aura Gnarlid gets +1/+1 for each Aura on the battlefield.

The List

Commander 2018

Planechase Anthology

Planechase 2012

Aura Gnarlid's second ability counts each Aura regardless of who controls it.

The power of each potential blocking creature is checked against Aura Gnarlid's power only as blockers are declared. Once a creature blocks Aura Gnarlid, increasing the Gnarlid's power or decreasing the blocking creature's power won't undo that block.