"Kitty," as she calls herself, often shows what could be construed as a form of "mercy"....though the motivation behind it has nothing to do with an actual desire to be merciful. She is motivated by a need to experience the thrill of challenge; something that for most of her life has been illusive and foreign to her as a result of her vast wealth/monied family name, genius mind, and extremely strong special powers. Being born with both nature and nurture that assured she never had to work hard for anything, she is an exceptionally spoiled and bored person who sates her boredom with games. Everything in her life she frames as a game, and as a result she will often artificially limit herself and even purposefully give her enemies advantages over her just to make the "game" more engaging. On the surface, this looks like she's trying to give her enemies a fair shot/assure even odds. However, its very much selfishly motivated by her own desire for pleasure/a cure to her boredom, and not out of any goodness, code of honor, or belief in fairness.
If your villain was born into a position of wealth and/or power (I.E. being royalty, a corporate heir/heiress, a deity or chosen of a deity, a super with very strong powers, an innately strong/powerful magic user etc...) would they still have grown up to become villain if they where born into a working class or even poor family, and with significantly weaker or even no magic/powers?