Killer Instinct

Easily done. In the Shadow Lords Hub, under "Guardians", you'll be able to recycle (or "transmute") your guardians into energy or "feed" them said energy to refill their use. Each guardian has five uses, with one consumed each match they're used in, NOT how many times they're activated per match. Simply focus on the repeated use of a single guardian, then feed that guardian 500 unites of energy over time. Does NOT need to be done all in one feeding. I did this using an Epic (i.e. purple) Vampire Bat, who cost 60 units of energy for each refilled pip, as the rare guardians cost more to refill and will thus net you the achievement faster.