Final Fantasy XIII
Start with two Sabs, that should give a good boost to the gestalt meter up to start with. After 2ish rounds of that, switch to Sab/Sen. As soon as they go yellow health, paradigm shift to Medic/Sentinel class. The Eidolon seems to goes through stages of attacking and charging. When Hecatoncheir charges, switch to RAV/COM. Just remember to switch back to a Sentinel role when the Eidolon starts to attack again.