As for Entropy, it looks like a Winged Rainbow off an Air Mark could work. Give it 2 purifys and 31 card to deck out Pandebonium, Wings + Nova can counter Discord, and Wings also works against Golems/Graboids. The only thing it would lose to would be a Stall larger than it, but Entropy might be hesitant to run a large deck in Round 1. If you guys like this idea I can have a code ready tomorrow.
For Water, I think an Earth Stall with EQs could work well. I'm hesitant to reveal so much of our vault in just one game, but everyone knew we had an Earth Stall anyways, no?