Strangest? I see a lot of stranger teams on my lower level account. A lot of them just look like they mashed together whatever the highest rarity troops they happened to have at the time and hope for the best.
In high level PvP, a lot of people have their low score or throw the match teams set, which accounts for most of the "strangeness" - single shrooms, villagers, bombots, etc, some of which might even have a chance of winning 1v4 against lower level opponents due to matchmaking. I've also seen some creative teams that can occasionally be nasty if you underestimate them, too, but I think it would ruin the novelty of facing them if I shared them here.
However, sometimes, it just looks like they are trying to have a strong defense, but just don't quite have all the pieces for the "meta" team and decide to make a little substitution. One that gave me a chuckle was Manticore, Manticore, Deep Borer... Keeper of Souls. So close, and yet so very far.