[Critical Mutation] (in empty slot) applies 300% critical chance and 300% critical damage at max stacks.
The crit chance actually applies twice to the grenade:
31% x (1+ 200% + 300%) x (1 + 300%) = 744% (Tier 7 Red Crits)
Multishot currently does NOT affect the Grenade or the AOE at the end of the beam (?bug).
Primed Fulmination does NOT affect the Grenade AOE (?bug)
If you can offload fire rate (eg reinforced bond, arcane velocity, wisp/[Harrow] fire rate buffs), swap [Anemic Agility] out for [Primed Target Cracker].