Burn and poison effect

[Zechnophobe]

So yes, spells, and Phoenix's both will do a good burn/poison damage, as will large stacks. With full Medal Bonus (Which you will very likely get early on) you will do 6.5% to 13% stack damage per turn for three turns. This is a median of 9.75% damage by the way, and over three turns will do, on average 26% of the stack's health in damage.

That's a pretty good chunk!