Hoard of the Rainbow Dragon

Hoard of the Rainbow Dragon enters the battlefield tapped, unless you control a dragon.
{t}: Add one mana of any colour.
{4}{t}: Add {w}{u}{b}{r}{g}.
{4}{w}{r}{g}, return a dragon creature to your hand:
Hoard of the Rainbow Dragon becomes a 10/10
dragon creature with flying and burn 5 that has
all colours until your next turn.