In Kessig, even celebration wears a fearsome face.

Hedgewitch's Mask

Equipped creature gets +1/+1.
Equipped creature can't be blocked by creatures with power 4 or greater.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Innistrad: Double Feature

Innistrad: Midnight Hunt

The blocking restriction is applied only when blockers are declared. Once a creature equipped with Hedgewitch's Mask becomes blocked by a creature with power less than 4, increasing that creature's power won't cause the equipped creature to become unblocked.