- Each deck may use 6 upgraded cards
- You may use Pillars, Pendulums, Mark Cards, and Marks that don't match your 3 elements (they don't count as using the element)
- You may not use the same combination of elements more than twice in a match.
Commenting on three changes: I like upgrades for changing the meta around quite a bit.
Pillars, pends and mark cards from elements you don't have do not count as using those elements, but pillars, pends and mark cards from the elements you do have count as using the element. This is oddly worded, but it has to be this way or else I could easily make monos (e.g. 10 aether pillars and 20 aether cards would be legal otherwise).
I don't like the sounds of this third added rule. It forces you to use your battle element at least once, which increases the RNG impact and reduces the importance of versatility within your own elements. I don't like having less strategic control and more RNG, basically.