New card. Alex! You have an encyclopedic-level knowledge of MTG cards. I know the name exists, but has this effect been done?

It's very similar to Rethink, although not quite the same (this one requires the mana to match colours as well). Also reminds me of Soul Tithe and Pendrell Flux.

Changed to (((Psionic Feedback))) because Feedback is a thing.

Currently testing hyper Mana Leak to avoid "counter target spell unless i pay its mana cost.. but i already paid its mana cost!". Now slightly less flavorful, slightly stronger, much simpler.

I think changing this to the mana leak wording is a good move. Consider that Mana Leak is now considered slightly too powerful, maybe just make this a Mana leak with the UU casting cost.

Another option is to add an additional cost to it, something like: "As an additional cost to cast ~, remove a Psi counter from a permanent you control. Counter target spell unless it's controller pay ."

Though at this point it might be worth reducing the cost to just or increasing the tax.