The power of each creature is checked only when blocking creatures are declared. If a creature has power 1 or less at that time, it can’t block, even if its power was greater than 1 when the last ability resolved.
2011-06-01
Creatures with power 1 or less can’t block even if they weren’t on the battlefield when the last ability resolved.
Haste
Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
Whenever this creature attacks, creatures with power 1 or less can't block this turn.
