I think a big factor in trundle's kit is the fact that he bears a curse designed to affect an entire tribe of trolls with powerful regeneration abilities by himself. With that much powerful magic in one creature, he has to have some power of his own from it (not to mention his incredible regeneration abilities, god-worthy tolerance of pain, and overall trollness) which can be seen in his ability to control the disease and affect others, terrain, and strengthen himself with it (pillar of filth, contaminate, and agony).
I actually think Trundle's lore is one of the best lores of LoL. Because he's born with amazingly natural talent, he's basically punished for it. Severely. He has to live with the constant agony of his flesh melting away then growing back in a never ending cycle. Yet he keeps going, driven by the knowledge that if he dies, the curse that he bears would most likely go back to the tribe, and goes into the League of Legends (as a troll mind you, next to some of the most civilized/powerful races in Runeterra) and stands toe-to-toe with legends, monsters, and magic incarnate. Trundle has every reason to hate life and give up: having to deal with the prejudices that the rest of the world has against him being a troll, bearing a curse while the rest of your kind gets off completely free, and being held back from your true potential of basically being immortal. Yet he keeps going, marching to the beat of a tattered, yet still valiant drum (haha, get it? beat?).
tl;dr - get out of the lore section.