Toad is a sniper in "Loose Ends". Wearing ghillie suits, he and his partner Archer provide sniper support as part of Task Force 141's Sniper Team One. He maintains radio silence throughout most of the level.
As revealed by radio chatter shortly after the mortar strike kills Ozone and Scarecrow and injures Roach, Shadow Company was aware of Toad (and Archers) presense, and called in counter snipers with thermal vision to dispose of them.
They were both killed by these counter snipers mere moments before Shepards betrayal, leaving them unable to warn or save the duo.