Radiation and cold. Radiation (+75%) and cold (+25%) do bonus damage to alloy armor, and 25% to corpus robotics. Radiation loses damage against shields (-25%), but cold does bonus damage to shields (+50%). So well rounded for both corpus and grineer. Will struggle against high level Heavy Gunners and other heavily ferrite armored Grineer however.

No exilus mod here, but if you want to forma this thing's last slot to get one, I'd suggest [Cautious Shot] so you don't flinch as much up close.