Creature aura pre-rendering
The major thing this week was making better Diablo 2-style auras but not rendering them dynamically; instead, I made a simple editor tool (based on this) that bakes auras as texture animation, bundling everything up as a texture atlas and using that. Made the in-game aura rendering code far far easier, than having separate shaders for each. Since each texture atlas supports up to 2048 animation slices (due to texture array limitations), for 64 frames per animation I can store 32 different auras, which I think is more than enough.
Another feature that I'm in the process of adding (added, bugged, debugging now) is freezing levels when you leave. First of all, freezing is important, otherwise if all the entities from all levels play, well that just doesn't scale. So, to avoid a boring "freeze immediately" after you leave a level, at the moment I allow for 10 standard actions (a minute in "game time"), which allows entities to suffer repeated effects, move a bit, etc.