Sower of Temptation enters the battlefield and causes me to gain control of a creature, let's say a Raging Goblin for example, as long as Sower remains on the battlefield.
I have Teferi's Veil in play and on the following turn, Sower attacks and then phases out.
When Sower phases out it is "treated as though it does not exist", but it is still on the battlefield technically. So it "remains on the battlefield" but it "doesn't exist".
So, when Sower phases out, do I lose control of Raging Goblin?
702.26b If a permanent phases out, its status changes to "phased out." Except for rules and effects that specifically mention phased-out permanents, a phased-out permanent is treated as though it does not exist. It can't affect or be affected by anything else in the game. A permanent that phases out is removed from combat. (See rule 506.4.)
Sower of Temptation phases out but does not change zones, so it "remains on the battlefield". It's treated as though it is not on the battlefield though. So I guess this means it does not actually "remain on the battlefield", maybe?702.26d The phasing event doesn't actually cause a permanent to change zones or control, even though it's treated as though it's not on the battlefield and not under its controller's control while it's phased out. ...
702.26f kind of seems relevant but the continuous effect is affecting the Raging Goblin, not the Sower itself.702.26f Continuous effects that affect a phased-out permanent may expire while that permanent is phased out. If so, they will no longer affect that permanent once it's phased in. In particular, effects with "for as long as" durations that track that permanent (see rule 611.2b) end when that permanent phases out because they can no longer see it.
I'm leaning towards "I lose control of Raging Goblin" being the correct result, but I'm not 100% sure.
Along similar lines, let's say instead Sower and Raging Goblin attack and phase out simultaneously. Next untap step they phase back in. Do I retain control of Raging Goblin?
I've never run into a game that had phasing and a continuous effect interact in these ways before, but I have a deck with both Sower and Teferi's Veil so the potential is there.