Can Aquamoeba beat Glory Seeker with discards?
It used to be the case that you could do this:


Declare attackers and blockers
Activate the Aquamoeba's ability
Resolve the stack
Put 3 combat damage on the stack
Activate the Aquamoeba's ability again
Resolve stack


This would cause the Aquamoeba to have 3 power when damage was assigned but have 3 toughness when damage was resolved, killing the 2/2 but leaving the Aquamoeba alive.

However, changes to the combat rules for Magic 2010 were made that specifically prevented this. Now damage does not use the stack and is assigned and applied in one step, so the Aquamoeba can be either 1/3 at the time (and both survive) or 3/1 at the time (and both die).