I posted this already in the champions section and realised it might be better placed here.
I've tried a few games with her, and her explosive shot doesn't seem to cost mana. It's marked as having an active, and a passive, and it costs 50/60/70/80/90. I've tried it out many times and checked my mana carefully. Neither the passive or the active takes the mana. I've also been able to cast it when I had less than the written required mana. So either it should cost mana, or the description of the skill should be changed
And if this has already come up and I missed it, sorry.