There is a type of crash that can happen with too many units in the game, or too many units going active then getting split across map sections (as can happen at the satyr war camp, where the first half of the camp is divided from the second half). So, whatever's happening in 800x600, it's not the result of that. However, if you fight murderbunny, there's no limit to the number of maggots he can spawn, and if the fight goes on too long, lag will be the biggest enemy.
Now, as far as entering the source of all evil and suffering, Less has a chance to equip Pandora's Box, which will, when equipped, spawn 2 random monsters, and will continue to do so every time one of them dies. There's something strange that happens to monsters that are in another section when active; the game like takes them into some weird state where countdowns can get messed up. If you get plague on monsters, for example, then shuffle back to another game section, the plague will continue endlessly on those monsters (this will cause a crash in multiplayer). I don't know how it will effect something like Pandora's Box that uses a spawning class otherwise unused in the game.