One of the better ideas I have seen, sort of. Although the example cards are, in respective order, under powered, over powered, and overpowered.
I don't really presume to know enough about the game to say I could make balanced cards. I just wanted to show two things:
1. How to potentially restrict cards to just one element. The best way I could come up with was requiring a minimum number of pillars on the table to play a card. I suppose there could be cards that could be "Can only be played if your Mark is [Element]", which would open them to be played by Duo or adjusted Rainbow decks. I guess "Cannot be played if more than 5 Quantum Pillars are in your possession" is also a possible condition.
2. Element restricted cards should be relatively strong. The point is that each element has a weakness, so each element should have a strength that can be used
only if you devote a chunk of your deck to that element. For example, you said two of my cards were overpowered, but you have to consider that those two cards will only be played in decks with a time or water emphasis. For the Unmoved Mover, even if it can remove immortal/immaterial status, the ONLY cards that element can target creatures with is Reverse Time/Eternity or Scarab (which might actually be useful then). So it's not like you're going to be able to remove immortality and then Firestorm/Ice Bolt/Twin Universe everything. For Water, playing something like Tidal Wave doesn't change the fact that you have a disadvantage in direct creature damage.
I think the Rainbow mindset is becoming too ingrained in this game, and even as a newer player I can see it getting boring. My objective here was to create cards that make Mono or Duo decks more powerful, but only at the expense of also accepting their weaknesses.
Right now, "Creature Control" means throwing another Firestorm, Freeze or Oty in your deck, and "Permanent Control" means another Steal, Pulvy, or Explosion. That's changing a whole 6 cards out of 30+, and not exactly deep strategy. Poisoning is so weak it can be ignored for all but 1 or 2 FGs. Why can't we build whole decks around Permanent Control? Why isn't Fire strong enough to consistently win on Spells alone? Right now, any decks that even come close to this are "just for fun," and anyone will tell you they don't stand a chance against FGs or Rainbow Decks.
I'll get off my soapbox now, but I think this game has a lot of potential that it's not tapping into.