Beguiler of Wills has an activated ability that gives you control of a creature with power less than or equal to the number of creatures you control when the ability resolves. In order to play this ability, its target must be legal and you must have an appropriate number of creatures. This ability also checks when it resolves to make sure that this condition is still true. If it is, you will gain control of the targeted creature.

There is no duration for this effect, so barring any other change of control effects, you will maintain control of the targeted creature until it leaves play or the game ends. Additionally, unlike many other similar activated abilities, there is not a restriction or limit on reusing Beguiler of Will’s ability. As long as you can tap it to activate its ability, you can continue to steal other creatures.