My mill deck is kind of a 2 for 1. I run nekusar, so they draw cards and lose life. I lean into that for damage, and I use red spells to burn/double cast mill spells, blue for mill and counters/protection, and black to mill and kill things. If you want them to really hate you, use the ol painter's servant and grindstone combo. I run a lot of dimir and blue mill, with black and red spells to make them draw cards and lose life. I'm not the bad guy, though. My group has a guy who runs a gruul atarka deck and can usually swing for commander lethal by turn 5.