What makes Shyvana so good?

Extremely fast clears, innately high damage so she can build near full tank and still be relevant, passive that gives resists even if it is awful, very low cd ult

insane clearspeed and good dueling which usually results in getting an easy lvl and gold advantage over your opponent. If you are any decent at keeping track of the opposing jungler, this allows you to shut him down rather well amd increase the lead. She's also rather good at pushing out sidelanes and soloing drake. All those things make her really strong for soloQ.

However, her teamfighting(like that of any bruiser) is pretty bad if she ever falls behind or carries get 4+ items and she offers little gaking preasure.

Also great pusher.

She's particularly stronger since the Season 7 additions of AD scaling to E (Both the initial damage and the burnout mark damage). She used to require much longer engages and relying on auto attacks to kill. Now her E skill shot is kill viable too, and deleting people in less time than they have to react.

She received a huge buff without ever really losing anything to balance it out.

Clear speed lets her farm and counter gank. She also has pretty good dueling power against other junglers.