While not single bosses, Vek Nests and overwhelming swarms can function as boss-like encounters. Nests continuously spawn new Vek until destroyed. Prioritize destroying nests, especially if they are spawning dangerous Vek. For swarms, use area-of-effect attacks and push abilities to control the crowd. Environmental hazards are your best friend here. Don't let yourself get surrounded, and always keep an escape route open for your mechs. Sometimes, sacrificing a mech to clear a path is necessary.
