Spectral Adversary

Any continuous effects with a "for as long as" duration ignore phased-out objects. If ignoring those objects causes the effect's conditions to no longer be met, the duration will expire. For example, phasing out Mind Flayer will cause the duration of its continuous effect ("for as long as you control Mind Flayer") to expire.

After you pay the 1 generic mana blue mana cost one or more times, a second ability triggers and you choose the targets for it. Players may respond to the new ability at that point. As that ability resolves, Spectral Adversary gets its +1/+1 counters and the target permanents phase out.

If an opponent gains control of one of your permanents, that permanent phases out, and the duration of the control-change effect expires before it phases back in, that permanent phases in under your control as that opponent's next untap step begins. If they leave the game before their next untap step, it phases in as the next untap step begins after their turn would have begun.