Convoluted Planstone

Whenever something is chosen at random, each opponent loses 1 life.
{u}{b},{t}: Choose a card you own in exile at random, return it to your hand.
{r}{w},{t}: Choose an opponent at random, exchange control of creatures. After this phase, there is an additional combat phase.
{g}{c},{ut}: Choose a land on the battlefield at random, tap it. It becomes a 8/8 colourless golem creature with trample.