This is pretty cool, I'd be down with this showing up in elements. hmmm instead of 'priest' how about.. 'mystic'. The entropy cultist hmmm.... 'Entropy cultist' is probably a perfect name for it because that's exactly what it is.
Now i know you probably want some help making your card ideas better and balanced.. sooo.. I'm not sure anyone who deals with an entropy deck is going to want to randomly convert their own quantum, maybe there could be something better. Well, actually, you know how entropy is random and all, and improved mutation grants a random bonus in attack/defense, perhaps this 'entropy cultist' could grant a rand increase/decrease in target creatures attack and defense. Its completely random, and that's what entropy is all about. It seams that this type of creature should be able to do this kind of thing anyway.
The darkness cultist... the idea of the ability makes sense, its pretty cool too, and not to sound offensive but I'm not sure the ability is of any real use. The only thing it could help would be to save its fellow darkness creatures from floods. When i think of darkness, i think of shady deeds, manipulation, deception.. An interesting ability would be to 'possess' target creature untill the end of the turn. This would be as though the fading cultist turns the opponents creatures against him/her for your attack phase. This would be pretty powerful. Another option is to change target creatures element to darkness, their ability now costs darkness instead. Both of these together would be a sick card, perhaps too powerful so.. maybe it'd be good to pick only one of them. These are your ideas, I'm just sharing possibility, do what you will with my ideas. =]
Maybe with the water and time cultist abilities, the effect can vary between targets. Say I target one of my creatures with the time cultists ability, it attacks twice, or does 50% more damage... but targeting the opponents creature would half its damage. As with the water cultist when targeting your own pillar (if thats how it would work) it doubles quantum production for 1 turn. But used on an opponent pillar it would decrease production by... 50%? I think it could work well this way.
The earth cultist is a little shaky, i'm not sure whether its ability is a good one yet or not, but its still pretty cool. As for the rest, I think they are all sick ideas, the whole theme... its good. You would get mad props for this idea if you could pull together some artwork.