Looks like callbacks are lost on restart.

As far as sanitizing, do you have your entity table in the sanitize_<mapname>.nut file? My mutation isn't map specific and it doesn't check non-mapmodes for the sanitize table, so what I did was just define my SanitizeTable in my mutation script and call it myself during OnGameplayStart()

Mine is only converting pipe bombs and vomit to molotovs, healthkits are moved on mapspawn

I've noticed running my mutation on stock maps that some items are spawned as "weapon_molotov" instead of "weapon_molotov_spawn" etc, the non-spawn variants can't be picked up, at least not by a human player.

Squirrel threads are like co-routines. Functions that yeild at point in execution and can be resumed. They work in l4d2.

From what I've seen (and the way I'm referring to it) nexthink is just the next time to think, so for something you were trying to animate you could set it to 33ms to get 30fps instead of 10fps.

Haven't seen one for that, but I did notice a few oddities
player_hurt fires an extra time after a player kills another player but passes attacker and attackerentid both 0

Also weapon_out_of_ammo doesn't seem to fire when viewing with display_game_events

Same with tank_killed

I decided on a coop mutation I tried with the original system but really couldn't pull it off. It's called Tank Slayer. All temp health, tanks out run you, killing tanks awards more temp health, tanks get successively stronger, spawn faster, health decays quicker and quicker, pills are awarded at various levels.Penalties for being a coward and kiting. Score is kept. Some other bells and whistles I'm working on. I figured it was a good excercise to utilize the new functions and event handling

A few other things that have come to mind

player.IsDead()

From Portal2
int CBaseEntity::entindex()

Maybe functions for SetParent SetParentAttachment, but you can work around those with DoEntFire

Also would be nice to be able to play non-game sounds on an entity.

Setting nexthink on an entity
I don't know if it's possible on an individual basis. 10fps for trying to manually animate something is very choppy. And many things don't need to think very often at all.

I know in Portal2 you can bump up the limit for all.

It would be handy indeed