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Have some comments:
Butterfly's effect feels weird outside
and it would be better not to have synergies spell'd out in the card text imo (BE activating it). Feels a bit OP as it is a bit like upped panda with a clause that allowa you to use it again (the 1-6 targets factor helps balancing, the PC side doesn't). The cost is a little higher than panda though.
Reaper has more synergies still. Innovation, Hourglass, Burn Card, Clepsidra and Yoink for example. I feel like sanctuary effects should block it. I'd rework the name to fit the theme a bit. In terms of balance I'd probably reduce the attack a bit (4/1 - 7/1 maybe).
Mural's name invokes a permanent to me, might wanna change that. It looks like steal on steroids, since you don't have to pay for it (quanta or health) to get the effect on draw or on discard (you can even control the discard with innovation), so it is seriously OP. The drawback is easily avoidable too by not playing the card)
I'll think of some cards too.