Nest of the Beasts

Titanfall - Whenever a creature or vehicle with
base power 5 or greater enters the battlefield
under your control, put a charge counter on
fortified land.
Fortified land has "{t}: Add {c} for each charge
counter on this land. Use this mana only to cast
Dragon spells or activate abilities of Dragons."
Fortify {1}{r}{r} ({1}{r}{r}: Attach to target land you control. Fortify only as a sorcery.)