Answer:
1) Scale.
2) Bite/Daze.
3) Pierce if Bite was used, skip this step otherwise.
4) Burn.
5) MegaBurn.
6) Scale if Pierce was used, Mana Regen otherwise.
7) Mana Regen if Scale was used, Scale otherwise.
8) Coil.
9) Repeat steps 4-8, using Breath instead of Burn/MegaBurn when low on Mana (I'd say >3000, but it's your call), until the Guardian Dragon is defeated.
If it says "It looks like he's preparing for a big attack", do this:
1) Breath.
2) Daze if the Guardian Dragon has not done its Breath attack yet; if so, return to normal strategy.
3) Roar if the Guardian Dragon has not done its Breath attack yet; if so, return to normal strategy.
4) Coil/Mana Regen in preparation of the Breath attack; return to normal strategy.