Okay - to start, some context. There's typically two approaches to CB. You either build a team with unkillable/block damage, which typically involves some pretty elaborate manipulation of turns through TM boosting, or you build a "standard" team. In the former case, your goal is to reach the minimum speed requirements, and then max out on damage. In the latter case, you almost always need some combination of Ally Attack or Counter Attack, or both, and the goal is to survive as long as possible - sometimes well over 50 turns (one of my early 1-key UNM teams routinely lasted 60+ turns).
You don't really have any pieces at all for the unkillable/block damage one, so we'll focus on the second option.
You happen to have both an Ally Attack and a Counter Attack champ, so we're going to make use of both. All champs below should be between 170 and 189 speed (after masteries/setbonus/etc):
- Fatman (ally attack) - a3 prio. on NM, a3 1 turn delay.
- Versulf (leech + ally protect) - a3 prio. on NM, a3 1 turn delay.
- Riho (block debuffs + all debuffs) - a3 prio. on NM, a3 1 turn delay.
- Skullcrusher (counter attack, ally protect) - second slowest. on UNM, a2 2 turn delay.
- Corvis (buff extend + debuff extend) - slowest. a2 prio. on NM, a2 1 turn delay.
Our goal here is to run double ally protect to keep the team alive, and rely on Corvis extend to keep the buffs and debuffs permanently active.