Terry, Hungry Wolf

Buster Wolf — Terry, Hungry Wolf gets +X/+0,
where X is the highest mana value among instant
and sorcery spells you've cast this turn. If X is
three or higher, it has first strike.
Power Geyser — {x}{r}: Exile the top three cards
of your library. You may play instant or sorcery
cards with mana value X or less exiled this way
without paying their mana costs until end of
turn. Activate this only if Terry, Hungry Wolf
is attacking.