Bengals star Joe Mixon went all out for his first playoff game ... ordering more than $400k worth of jewelry to commemorate the big day!!
TMZ Sports is told ... the Pro Bowl running back wanted to do something extra special for his first postseason appearance, so he hit up his go-to guy Gabriel The Jeweler last week to whip something together.
We're told the order -- a special made Cuban link chain, iced-out Audemars Piguet, and diamond ring -- would usually take about a month to complete .