LINKS! Please! Now i have to look through all the card ideas to comment on Theta, that's silly!
I'll just comment here then, your fault: I would add the following text to Theta, as a nerf, but i realize it would also be some kind of deck management benefit, anyways here it is:
"Unique: remove all Thetas from your deck."
That makes sure you can only use it once, could be a new way to balance some strong cards. That could allow a cost reduction aswell.
It has the benefit however, of reducing your deck size by 5 instantly, making your remaining card types more likely to be drawn.