Aurification

Whenever a creature deals damage to you, put a gold counter on it.
Each creature with a gold counter on it is a Wall in addition to its other creature types and has defender. (Those creatures can't attack.)
When Aurification leaves the battlefield, remove all gold counters from all creatures.

Acorn Catapult

{1}, {T}: Acorn Catapult deals 1 damage to any target. That permanent's controller or that player creates a 1/1 green Squirrel creature token.

Aerial Modification

Enchant creature or Vehicle
As long as enchanted permanent is a Vehicle, it's a creature in addition to its other types.
Enchanted creature gets +2/+2 and has flying.