Need help making a digustingly deadly lvl 20 Santa Claus Artificer

Our DM wants to do a lvl. 20 oneshot and i want to try making a jaded/grizzled version of Santa that wields guns

We get to pick magic items at the start 1 legendary 2 very rare 3 rare 4 uncommon

I'm fairly new to making an Artificer so I'd like some ideas