u/Miserable_Lychee_629

I remember the pool being in a dungeon or cultist hideout and it was in the middle of a desert. The magic system was also based around specializing in a "core" or type like blood, shadow, water, electricity, etc that you could obtain through consumed items or tasks. You could also only have one core but could combine another one into your own and make a hybrid core like fire and earth making a lava core. I'm like 90% sure I didn't dream this one up but I cannot find it for the life of me despite trying multiple times. I think the MC was a former military member in his original world as well.