Respiring Sentinel

When Respiring Sentinel enters the battlefield,
create four 1/1 white Human creature tokens
with haste and desertwalk. Exile those tokens at
the beginning of the next end step. (A creature
with desertwalk can't be blocked as long as defending
player controls a desert.)
{w}, Tap an untapped desert you control: Until
end of turn, target land an opponent controls
becomes a Desert in addition to its other
types.