Xarinia, Alterer of Space

Xarinia, Alterer of Space gets +X/+X, where X
is equal to the absolute difference between the
total power and total toughness among creatures.
{2}{u}{r}, {t}: Draw any number of cards equal to
or less than Xarinia's toughness, then discard
that many cards. Put a -1/-1 counter on Xarinia.
"An object in motion stays in motion unless I say
otherwise."