Oracle Text

Vigilance, trample

Whenever Meglonoth blocks a creature, Meglonoth deals damage to that creature's controller equal to Meglonoth's power.

Card Rulings

2/1/2009 You don’t check Meglonoth’s power until its triggered ability resolves.
2/1/2009 If Meglonoth leaves the battlefield after its ability triggers but before it resolves, the amount of damage it deals is equal to its power as it last existed on the battlefield.
2/1/2009 If Meglonoth somehow blocks more than one creature, its ability will trigger once for each creature it blocks.