Counter target spell unless its controller can remember what those stupid symbols are? It's a reprint of Counterspell in disguise! :)

You just don't like new things, Vitenka. :-P

Forcing the opponent to use a specific mana to pay seems pretty brutal and will probably make this Counterspell in most cases. It's not a problem if you think Counterspell should be coming back.

A lot of decks have lands that produce colorless mana. There are certainly quite a few such lands in Standard.

Yeah, a lot of decks have lands that produce colourless mana. But a) this needs you to have two such, and b) it needs you to have them untapped. When it's generally more sensible to tap your colourless-producing lands first, to bluff cheap coloured instants. I guess now there are cheap colourless instants that's less hard-and-fast, but still.

If this said "unless its controller pays " or even "" I'd be fine with it.

Interestingly, this would be a lot more fair in Oath of the Gatewatch itself, because of all the Eldrazi Scions floating around. I still think would be fairer than though.

I designed it with the idea it would slot somewhere into BFZ and Oath limited, hence the utilization of mechanics from those sets. It would be quite strong in Standard and possible even modern, though.
I struggle with counterspells because of their costing. gets you unconditional hard counters in the form of Cancel. Sometimes that same cost gets you Dissipate, which is (usually) better. If this cost or , though, it would generally be worse than both of those. At or , though, it looks too powerful, even though it's conditional.
I'll edit according to your suggestion, Alex.

I feel like wizards rarely actually do "unless you pay M" instead of "unless you pay X" because it's too random whether your opponent happens to have it.

True, but I feel like colorless mana is a bit of a different case, since any deck might feasibly produce it.

It's extremely rare, indeed. Quenchable Fire was moderately recent, but that's basically a 6-damage burn spell with a random drawback. Mtenda Lion is the only one I can remember that doesn't have some other payment option (Norn's Annex accepts either or life) or some fairly likely corroborating suggestions that you'll be able to produce the mana (Heroism, Thelon's Curse).

Yeah, I agree requiring colourless mana is better than requiring coloured mana, but I'm not sure if I'd want to print this or not. Maybe make have an alternative cost so it's more like mana leak than counterspell? Or have it on a slightly smaller effect? Or this may be fine, obviously in this block it makes sense to push matters effects.