Let me tell you about those soul coins because they're absolutely fascinating in how they connect to our tiefling friend's story and abilities (this is one of those perfect examples of gameplay matching character development). The way karlach uses them ties directly into her past in avernus, which is why they're more than just power-ups for her.

When you find these coins - and there are only 20 in total so use them wisely - you'll notice they trigger something called infernal fury, which makes perfect sense given her infernal engine heart. During combat, this means extra fire damage when she's either raging or getting low on health, and after the latest patch, her unarmed attacks pack even more heat without needing those conditions (pretty handy when you're in a tight spot).

The really interesting part is how using these coins plays into her character development, since each one contains a trapped soul that gets destroyed when used. While this won't affect your gameplay mechanics, it definitely adds weight to your decisions about when to use them (might be worth saving them for those really crucial fights where the extra damage could turn the tide). Everything about these coins, from the moral choices to the combat benefits, reflects her struggle between survival and trying to move past her time as zariel's weapon - which is exactly what makes her such a compelling companion to have along.