"Aleister the Invoker" + 1 DARK monster If a player's monster effect attempts to activate, none of that player's monsters can activate their effects for the rest of this turn while this card is face-up on the field. Each player can attack with only 1 monster during each Battle Phase.
This card is underestimated. I run it in a Millenium Eyes Restrict/Invoked deck. Its effect of only allowing one effect and attack per turn can completely destroy your opponents strategy when used properly.