Just wanted to post this as a reminder. You can have only ONE global spell during a duel.
I was recently fighting the gearheads (storm) in Chelsea Court with my myth wizard. I cast the myth "Time of Legend" (global spell +25 to all myth spells).
Someone joined the fight, and they cast a "fire" global spell, which cancelled out my myth spell.
This was a previous post from Gamma:
Global spells do NOT stack. The most recently cast global spell will override the previously cast global spell. {o,o} |)_) -?-?-
Yep. Usually this is a bad thing, but can come in useful when playing PvP against death, or against Mordekai and his 1K minions in the haloween tower, both of which can use Doom and Gloom.