First off, I love the title "For the Swarm!" The theme itself was quite fun, and I loved the horns. It starts a little abruptly (maybe resolvable through sound mixing) and I feel like it needs to transition at some point in the middle to a more flowing theme to give it more texture and keep it from becoming stagnant. Otherwise, great piece! The little chime like dings were enjoyable too, if not a little too upbeat for a game about an evil necromancer, haha.
That demonic voice for the "under attack" SFX though is FIRE! I love the way you edited it and wish I could have gotten a similar effect with my undead voices. The roar had the same vibes but did not sound much like a roar. I would suggest reducing the distortion a little bit to let the roar shine through. Finally, the death sound is fun, but it almost sounds like they fell in water? Would be cool for a dark slime or ichor-based creature like little Venom spawns.
Great work on this!