I’ve been focused on the Challenge mode, and I’ve found this combination that is fun, but hard to pull off.
In Challenge mode, one of the Heroes is the Reaper. Usually a high level Unit, but in Challenge, its been promoted to a Hero. Its a flying unit that deals poison damage, but it has one ability. Reaping - attack a unit with under 120 hit points, and deal 1000 damage.
On the face of it, only really good against super armored units, but it works with Boomerang.
Now, Boomerang is a terrible weapon. It reduces your damage by 50%, but attacks another nearby target. Only good if the purpose of your attack is to deal penalties, like poison or freeze. But it works with Reaping. If two enemy units are next to each other, and you can reduce on of them to 120 hitpoints or less, Reaping will deal 500 damage it, and the target next to it.
Its not easy to pull off, so I don’t think its O/P, but interesting.
One thing of interest though, if you level up Reaping, the damage limit goes up. At level 5, I can Reap anything with 150 or less hitpoints. So, it seems, 6 hitpoint increase per level (you start at level 0). Not super easy to pull off.