I would argue that a combo of Houndoom and Toxicroak is best for that particular trio. They cover each other's weaknesses beautifully, with Houndoom taking the Fire and Psychic type attacks aimed at Toxicroak, and Toxicroak absorbing the Water and Fighting type attacks aimed at Houndoom. That, along with their STABs dealing super effective damage to two of the three (Venusaur and Registeel) and the fact that each of the three has difficulty dealing much damage to them in return without risking being KO'ed is as close as your going to get to perhaps anti-metagame regarding those Pokemon.
It sounds great on paper, but I have no idea how this actually works in principle.