I still don't think you understand the rules regarding flying and guarding. A Flying creature that decides to guard is grounded, and thus able to be attacked by melee creatures. A Flying creature that attacks a guard has to swoop down within melee range to attack, so is able to be counterattacked by any guard. So having Flying on a guard is unnecessary to fight Flying creatures. You only need Flying to fight Flying if you're both in the air.
Therefore, you should just remove the stipulation about guarding from Gargoyle and just make it "during your action phase, Gargoyle becomes a creature with -5 armor and Flying." You might also need to specify active creature, since conjurations do not get an action marker.
Therefore, you should just remove the stipulation about guarding from Gargoyle and just make it "during your action phase, Gargoyle becomes a creature with -5 armor and Flying." You might also need to specify active creature, since conjurations do not get an action marker.