Meglonoth — ruling 1

You don’t check Meglonoth’s power until its triggered ability resolves.

Meglonoth — ruling 2

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.

Meglonoth — ruling 3

If Meglonoth somehow blocks more than one creature, its ability will trigger once for each creature it blocks.

Meglonoth : règles, fonctionnement et interactions (MTG)

Meglonoth is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Vigilance, trample Whenever this creature blocks a creature, this creature deals damage to that creature's controller equal to this creature's power.

How it works : Meglonoth

Original English text — Wizards of the Coast / Scryfall

#1February 1, 2009· Wizards of the Coast
You don’t check Meglonoth’s power until its triggered ability resolves.
No other card is named in this ruling.
#2February 1, 2009· Wizards of the Coast
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.
No other card is named in this ruling.
#3February 1, 2009· Wizards of the Coast
If Meglonoth somehow blocks more than one creature, its ability will trigger once for each creature it blocks.
No other card is named in this ruling.