So, I already have robots in my setting in the form of artifacts, from golems to the Antiochian Holy Hand Grenade. Artifacts, though exotic, are nothing more than advanced technology, so much so that almost all of them require molecular nanotechnology to be reproduced.
The problem is with Mephisto's Immortals. An army of at least 300 (juxtaposition intended) animatronics (humanoid robots in silly suits that might or might not be armor plates), some dressed as SS officers on top of that.
Aside from their creator's edgy design choices, they are fairly high quality and able to tank 2, if lucky, 3 point-blank shots from a .50 cal Barret and can use artifacts themselves. They have access to camouflage and have the option to be either remotely controlled or use their (more primitive) onboard AI, though they remain just as lethal.
Meph hates when people break his stuff, so expect countermeasures to be applied where physically possible and not extremely impractical.
Manufacturing animatronics requires molecular nanotechnology, their operation a plentitude of gasoline. Animatronics are water-resistant, their muscles are pneumatically actuated, there's an emphasis on making their communication untappable and unjammable.
So, how can a portable, dedicated anti-robot (as in next to useless against organics) hard-to-counter artifact work?