How to do Gain control?

[bellaxiemtg]

If I cast Slave of Bolas and gain control Talus Paladin, do I gain life with that?

[Tammit67]

Has the Paladin gained Lifelink?

Gaining control does not make a card re enter the battlefield. Gaining control doesn't mean it exits his battlefield and enters yours. It is all one entity.

So in order to gain life off of it, either you have to cast an ally after casting slave of bolas, or your opponent had to have flashed in an ally before slave of bolas resolved.

[Malchar]

If you gain control of something, it doesn't enter the battlefield again. The ability on Talus Paladin won't trigger unless you cast an Ally after.

[Tammit67]

If you gain control of something, it doesn't enter the battlefield again. The ability on Talus Paladin won't trigger unless you cast an Ally after.

Or if one was cast prior somehow