What happens if you discard a targeting CC card?
This might result in more desynchs as well unless we change the way your turn ends - not sure about that though.
I think the cost is alright. 4
then you wait a turn (it could get destroyed) and then you pay 2
...
This already requires a duo to pull off and its quite situational - though you could save up your cards in anticipation and play them for free. Lots of synergy with high cost Aether cards like Phase Dragon and easy to pull it off using fractal.
Hmm now that I think about fractal (sorry to bring up the "But fractal!!!" comment) this card could probably stand a higher cost.
If I play a vestige, wait a turn and then flashback I need only play fractal immediately thereafter on ANY creature - opponent or my own - and I can play 1 of those fractaled creatures for free. That is a little OP.
High cost seems better considering Fractal is in element with vestige...