If you don't control another creature with power 4 or greater immediately after Turret Ogre enters the battlefield, its ability doesn't trigger, even if you can raise a creature's power right away. If you control no other creature with power 4 or greater as the ability resolves, nothing happens. These don't have to be the same creature, though.

Turret Ogre's ability doesn't deal more than 2 damage to each opponent if you control more than one other creature with power 4 or greater.

In a Two-Headed Giant game, Turret Ogre's ability causes the opposing team to lose 4 life.