Variants of cards that have their caverns of time versions are not able to be put in deck in twist, despite theoretically being legal. For example, my Aya is not usable, because i have CoT version, and not the MoG one
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Also, Core versions of some cards (like EXPERT1 [1]) are not usable, you’ve gotta craft or otherwise obtain them if you wanna use them (I think there might be a topic or post about it somewhere here; UPD: here it is).
An oversight? Perhaps, but somehow, players have got to pay one way or another for these ‘oversights’, hardly ever the other way around (and if it happens, it gets fixed ASAP!!!1111 , even if game-breaking bugs have persisted for months — dat be priorities, mon). A coincidence? 
Let’s say I’ve some reasonable doubts about it.
That is just something to think about, and I urge you and other actual normal players (not rabid forum trolls, loons and white knights of the Enterprise) to draw your own conclusions as to whether this game is worth spending your resources, and money in particular, on it.
[1] See, for example, this for explanation.