Thanks for your support!
playing by downloading offline version may perform better than browser play
the performance issue catch is believed to be due to:
1. the physical ragdoll death effects that makes the game laggy, more lags when more enemies die at the same time -> performance hit
2. the bigger the map has been generated, the longer A* paths generated for every enemy -> performance hit
in order to fix the above 2, the game should:
1. allow users to toggle physical ragdoll death effects in a settings page. When physical ragdoll death effects are off, the dead bodies play their pre-defined death animations.
2. investigate how to treat A* path vector as grid units (thus decreasing calculation burden) there is actually a tutorial I remembered bundled with Godot that accomplishes Grid-based A* pathfinding.
If I am able to fix (1) and (2) , I can then literally double the map generation size (i.e. 10-20 rooms) and concurrent enemy count (I.e. a swarm of 20-30 enemy crowd would still be CPU-friendly).