Tip: Do not fight the money bag miniboss in Tartarus. It seems to be the more common of the minibosses in Tartarus, so best to avoid any exits with the skull beneath them while you’re there. If you decide to take the risk and end up in the same room as it: Keep as close as you can to the bag without being in range of the slow explosive coins. If you’re too far from it during its gatling shots, you haven’t a prayer of avoiding them.
When it’s doing its gatling shots, do not dodge perpendicular to the shots; instead, dash towards and slightly to the side of the moneybag, ideally so you end up behind it. Attack the bag while circling around it at a speed roughly equal to the speed at which it is rotating towards you; do not go too far, or the moneybag will rotate in the other direction, potentially catching you by surprise.
Once the armor is broken, attack nonstop until its dead.
If you’re not careful during this fight, the moneybag miniboss can easily claim more than one Death Defiance.