When you say counterjungling, do you mean stealing enemy jungle creeps? Or just killing the enemy jungle in their jungle?
Mundo is amazing for both with his ridiculously fast clear times and scary amount of early dmg (junglers dont run ignite too!).
I just started maining Sejuani and can successfully counter jungle ~1700 elo this season. Her w is like a Mundo W that doesn't eat into her health and her passive, slows, and burst make it so you can take out a weak champ early after level 3. She counters a lot of champs like Nautilus and Nocturne hard.
Also no one knows how to play against her so it's hilarious.