A good Dark Urge is basically
what I was roleplaying for a long time in the game, which back then was based around tadpoles, but I got really lucky as Larian eventually introduced this similar premise as an actual Origin story, so I ended up extremely happy and really loving Dark Urge

The idea always was to roleplay a good innocent soul that got forcibly corrupted and turned into a monster after some horrific rituals and procedures inflicted upon them, who eventually slips away from the clutches of their tormentors to rediscover the essence of their true self while fighting against the dark corruption that looms deep within them.
In this case my Tiefling Huntress was an innocent aspiring Ranger that got kidnapped, ripped apart and mentally faded away to the very outskirts of her mind where she remained imprisoned to give way for the obedient monster known as Dark Urge to prowl Baldur's Gate and rack an insanely high kill count until the mental walls of her prison broke because of the mindflayers. Her true nature at that point starts to slowly resurface again, but the damage is too great. Whoever she was as Dark Urge is not who she is at heart, but the darkness within her remains and now she has to fight against it in order to rediscover her true self or forever lose herself.
And the way it all connects into the story and especially with major villains really made it easy for me to just fill up the blank pieces of the story and enjoy it thoroughly.
Which is why my characters are always pale with dark purple highlights, to represent the corruption which remains due to the horrible procedures that were inflicted;
Also at the time due to how the Dreamer was being set up, I always made the Dreamer an exact uncorrupted mirror image of my character, to sort of remind them of who they were and what they should be striving to be once again. An example with my Drow at the time (ignore the goofy eyes

);
I enjoyed this idea a lot so I still use it to this day;