This card is indeed cryptic. If you know your timing, you can declare the lands you're going to tap as targets, before you have to tap them to pay . It would confuse a lot fewer players (and be more readily apparent as an all-upside ability, as R1s are wont to do) if it just said ": tap X target permanents", or more simply ": tap target permanent" dropping the restriction (if it's for X, why would you need to use it more than once a turn anyway?)

Fixed, but the card doesn't look as nice any more =(

This is like a super glare of subdual. Almost impossible to lose with this in play and they don't get rid of it.

I am a little wary about it being too good, but being a creature limits it's power in constructed, and being a mythic limits its presence in limited.

That said, if this card is pretty good, then there's certainly nothing wrong with that. It's set up to be one of the premier blue rares/mythics.