The greyest of them all is the mighty Karn. He has compassion and revenge in his heartin equal proportions. Indeed when Dinkar eulogised Karn and highlighted his dilemma in Rashmirathi, it was done keeping a balance of words. Else it would have been rejected.
The transition from Ramayan to Mahabharat is, according to me, a change of stand the devil took. It lost to Ram because it was concentrating on Ravan and with Ravan's death the game was over. So devil took a strategic step of diversifying the risk. It took longer than planned but now at the edge of Kaliyug when every human is a shade of grey, devil is finally going to have a ball.