The Amulet of Protection is a feature in GvG matches that protects the Guild Lord and prevents tactics that aim at ganking him quickly to end the match.
At the start of the game, the Guild Lord can take no more than 25 damage points per second. Over the first approximately 12 minutes of the game, the damage limit gradually increases up to 300 damage points per second.
If the Guild Lord takes damage that would exceed this limit, his amulet heals him for the difference. If the Guild Lord loses Health due to damage-over-time effects or other direct loss of Health, then once every second, his amulet heals him for the amount of Health he lost that exceeds the limit.
The limit increases at a constant rate of about 22.9 damage points per minute, starting when the game clock reads 0:00 and the gates open. The limit reaches 100 at 3:17, 200 at 7:39, and 300 at 12:00, after which it remains at 300 for the rest of the game.