Ultraportable nuke. Can be dropped down a staircase to clear out the level before you enter it, with obvious applications.
I think that the nuke we have right now needs some changes.
1* It should kill all the monsters and give us XP on the previous level, if we prime it and leave the level before it goes off... I can already imagine receiving a message "You suddenly hear a violent eruption !" on the level below...
As for implementation - calculate the XP for all the monsters left on the level, save that value when the level perishes, give it to the player either the same moment he enters the new level (east) or after the amount of turn it had left till explosion (minus the time needed to go down the stairs).
2* We should be able to turn it off by 'u'sing it while primed. (We... can't turn it off right now, right ? I never tried to...)
It might sound like making it more easy, but we would make a frantic run for turning it off possible and save a few marines whose invulnerability worn out just before the blast... Besides - turning something off just before it blows you into oblivion is always fun ;).
3* We should be able to drop it down to the next level, regardless of whether it's a special level or not. Would make the nuke useful regardless of nearby Inv Globes and would add some more possibilities. We would be tempted to drop it down, get the XP and not risk getting hurt, while also losing all the items and power-ups we might have recovered...
Implementation should be easy... Generate a level, place a nuke, blow it up, save the level... voila.