Shyvana is the New Nunu
She scales better than Nunu but you can shut down the enemy jungler in the same counter-jungling playstyle. In fact, she is way better at it than Nunu because she can use the ult. to escape over walls and she farms/takes objectives a lot faster too. Moreover, she scales better than him and can actually snowball effectively (no pun intended). Unlike Yi, there's no point where she's actually really weak and most games aren't long enough for Yi's better scaling to outshine Shyvana's greater gold income.
I really believe she is the most broken jungler outside of competitive play. She is also probably the only primarily Devourer jungler that I'd expect would be viable at their level (even though she hasn't seen play). Elise and Nidalee are objectively stronger than her but at least they require a lot more skill to be used effectively. Threads like this usually get downvoted hard, but time will prove me right. I'm not the type to get beaten by X jungler and then cry about how OP they are. She is currently the best performing jungler in Platinum+. While I don't think she's OP at the highest levels, I do think she needs power distribution tweaks to make her more manageable at lower levels or at least more skillful.
hardcounter her, and though
usually ends up getting crushed in lane, if vayne does decent she also counters shyvanna.
can stall out games and give her a very bad time in teamfights