Hm... if you do want to go with Egyptian mythology, Anubis might be a better fit for Kaiba personality wise. The ties to the underworld and being dead pharaoh's right hand, and could tie in the ability to judge hearts as a power somehow... then again, that might need permissions for player to player interactions.

Another option if you want to go for more reptilian/draconian is that there are... quite a few snakes in charge of guarding the sun god Ra on his nightly voyage. Overly Sarcastic Productions has a few nice videos on Egyptian mythology and underworld myths if you're interested.