Hi! I'm fairly new at examining decks (I have a recent thread in this subforum too haha), but here's my two cents:
First, you seem to enjoy using poison. You have several water-death based creatures, partially powered by your mark. I think you might want to reduce on those, unless they are definitely your main damage-dealers.
Second, what is that unknown card? The forum doesn't recognize it yet; is it a pendulum?
Third, you have exactly one hourglass. In order for hourglasses to be effective, you have to scale them with your deck size; you might want three or four or even five with a deck this size. Try to get upgraded ones ASAP if you like playing rainbow decks, because the decreased cost of triggering the effect is extremely important.
Fourth, do you find yourself having excess quanta? That looks like a lot of pillars for a deck with lots of low-cost cards, and with novas you should be able to take even fewer pillars. When you get the cash, towers are surprisingly helpful, even though they barely appear better than pillars.
Fifth, and this is the point I am least sure on: I think your deck might be stretched too thin in certain directions. You seem to have a bit of creature control, a bit of permanent control, a bit of quantum denial... Maybe you should emphasize one of them more or less, like the "CCYB (CC? Why Bother?)" deck that has been so successful recently (I use it. It's pretty fun but expensive to build).
I wish you the best of luck, and hope some players more experienced will help!
