Personally I like Serendipity and its random effects, and I think it 'can' be very useful with a composition that takes it into account. But I like this idea as well, and even if its not taken for time it'd be nice if it would somehow get put into another element, or perhaps another entropy card period. Perhaps it could instead be a non-shard permanent that just stayed on the field. Also, I like the idea that some cards become useless/detrimental. This way it serves as soft counter to spells and such while also giving benefits to those who build their deck around it. One of my only problems with it is that it auto-wins against any deck that relies on a lot of regeneration like SoG's and Sanctuaries and basically makes them unviable.
Anyway, a couple simple guideline suggestions to help complete the project if they work for balance. Things that need to be looked into intensively are separated although there might be balance issues.
All quanta drain becomes quanta generation, and most Quanta generation becomes Quanta drain like via RoL's and the original playing of Quantum Towers. Pillars should probably be unaffected by this unless the idea of a hand like (Snova+Snova+ 2 Entropy Pillars + Shard of Chaos + 2-3 creatures like Elite Grab+Flesh Recluse+Giant Frog) locking the opponent down at Turn 0 for the first 2 + however many other shards you can chainx2 turns with 0 way to stop it is intended.
All % chances are inverted.
Gravity Shield blocks all creatures with 5 or less HP.
Bonewall lets attacks through, but creates a bone wall for each attack that goes through.
Phase Shield lets through Physical Damage, but the turn counter goes up for each turn. (?)
Explosion TU's the permanent to the same player, Steal TU's it to both players. I only have Steal different so as to make it not identical to explosion, but exact copying would be.
Rewind Time turns a creature into a Skeleton, and rewinds skeletons into the deck.
Parallel Universe Rewinds. I say this mainly because what you suggest for Twin Universe I think should be for Quintessence.
Draw effects make the opposite player draw a card. (Potential combination with the fire shard that is rumored to force the opponent to draw cards, and screws over draw decks.)
All delay effects give the target Adrenaline, and Epinephrine delays the creature for a turn for each time it would normally attack. (4 turns for a 3 power, 3 turns for a 5 power, etc.)
Unstoppable delays a creature for 2 turns and takes away 1-1.
Boneyard creates a random non-death creature with a quanta cost of 5 or under. (Quanta limitation to prevent heavy abuse, but might not be needed.)
Things that are Frozen cannot be targeted instead of its usual prevention from attacking while the shard is in play.
Creature producing effects from creatures, such as Evolve, Hatch, Firefly, Scarab produce a mutant of whatever they would make normally. (Might need balancing, but I like this because it fits with the mutation theme in Entropy as well as I don't see any real 'opposite' to it, and it'd make for some very interesting mutation decks.)
... wow, that was a bit bigger of a list than I expected. Thats a good thing really.
