Overview
416's Mod fixes several of the issues with AP Grenadiers, most notably their 8 seconds ICD.
Mod I grants her an ICD reduction to 6 seconds, as well as improved base stats and Skill multiplier.
416's Skill 2 has 2 effects, depending on whether the main target dies or not. If the main target dies, the Grenade will cause a secondary explosion of 3x Damage with a 4 radius. If the main target survives, the main target will get 20% Vuln and take minor additional damage over time for 3 seconds.
This Skill 2 makes 416 very efficient and clearing out large groups of low HP enemies, even if they aren't all tightly grouped up.
Take note that even if 416 applies some extra effects on surviving targets, this does not mean she is a single-target Doll and she is not what you should be bringing to boss fights. You should consider her Vuln and minor damage over time to be bonuses, making her less terrible than most AP Grenadiers if you need 416 to clear the enemies in the way to the boss.