http://lucy.allakhazam.com/spellraw.html?id=21552&source=Live I'd guess (Appears to fit, but not confirmed yet) that there is a 100% (Base1 = 100) chance to proc http://lucy.allakhazam.com/spell.html?id=6355&source=Live (Base2_1 = 6355) when a spell is cast, a 225 damage -200 Fire Nuke, for as far as the 383 effect goes, no clue about the 348 (100/10/0) one though. Maybe a limiter on the chance to bring it down to 10%? Just a guess there.
EDIT: From a recent description of 428, looks like there's a minimum mana cost of the casted spell must be 10 or some factor thereof.