History of Cornered Flakes

Cornered Flakes ("Collect the Rare tonic Flake reagents") is an Episode: Revenant triumph tied to Tonics.

Rare Flake reagents

There are four: Volatile Flake (Episode: Revenant activities), Enriching Flake (earned in Onslaught Salvation), Tomb Flake (Tomb of Elders) and Reflective Flake (the Kell's Fall Exotic mission). The triumph likely means collecting each of these.