Target creature gets +1/+1 for each land you control until end of turn. Whenever that creature deals combat damage to a player or planeswalker this turn, put that many +1/+1 counters on it.
Equestrian magic constantly leaks into the human world, available to whoever can claim it.
deactivate. seems too likely to just instant-win, and green has way took many -1/+1 counters already