Is there any reason why there is no sleep weapons in the game? It is the only status effect that has not been added to a weapon either by charge or regular attack. I personally think it would be interesting. It would be simular to the iceburst brandish in which you can imobilize an enemy from moving.
However, I can see why this could be potentionally be a problem. In the wiki it says sleeping allows the target to regenerate health, which would be counterproductive for a weapon which is supposed to deal damage. If the sleep effect was on a regular attack it could possibly be too overpowered expecially one-on-one as the monster wouldn't be able to both move nor attack. However, these two problems could be fixed if the sleep effect only happened when used with a chargeup attack, as the chargeup attack wouldn't nessarrly require to deal damage and the sleep effect couldn't be spammed.(unless possibly with a party of 4 cycling through their chargeups with UV charge reductions)
Sleep is extreme when used together with poison.
A bomb that sets sleeping gas free would be awesome, but a 2 bomber team, one with that bomb, the other one with poison, could kill (nearly) everything without getting attacked.
They don't move, they don't heal.
Except for constructs and undead.