I have made around 20 unique AI systems for my most recent project. Here, we can see a couple of the highlights. I try to avoid using the A* pathfinding algorithm because I feel like it's common enough that it's recognizable at a glance. Instead, I opt for a system where enemies easily give up, and they have performant methods of avoiding obstacles.
Jungle Demon
The Jungle Demon is capable of controlling 6 legs that grab on to nearby solids. With an eye that choreographs it's intentions, the jungle demon is a difficult but fair enemy.
Leech Hordes
Leeches were design to be performant even when they surpass 200 in number. I use many shortcuts to ensure their efficiency- they don't search for new targets, they cast an attack box less often, and they turn into stone if they get stuck for too long among many other minor shortcuts.
Fungus
The fungus is a hive mind of individual blobs, which makes managing its behavior quite difficult. The fungus moves by destroying itself and growing toward its desired location, so object pooling was mandatory to keep instantiations to a minimum.