Two things - first off, I wanted to thank everyone who works on Forge. It's great ^.^
Secondly, I believe I encountered a bug/glitch and I thought I should report it. I was fighting a vampire deck using a green deck, and I had
Gravity Well on the field (which causes creatures with flying to lose flying when they attack until end of turn).
The opponent had
Vampire Nocturnus out, which gave all his vampires flying. When they all attacked, I couldn't block any of them using my creatures (none of my creatures had flying/reach). I assume the reason I couldn't block them is because they had flying (none of them had fear, intimidate, shadow, protection from green, etc; also, there were no enchantments/artifacts/etc that prevented my [untapped] creatures from blocking). [I assume the game did something like this:
Vampire Nocturnus gave them flying -> attacked -> lost flying ->
Vampire Nocturnus gave them flying again.]
If I'm wrong about this, please let me know! I might need to switch out
Gravity Well with something else if this scenario is actually legit.