A monster, probably in the y or e class, with an attack that steals an item (or a few items, excluding equipped gear) from your inventory and randomly teleports it somewhere on the same level. This makes object detection and detect treasure nice to use even after a level is fully explored.
Monsters with AT_EXPL kamikaze attacks are excluded from the regular is-this-foe-too-strong-for-me level checks. The point of those checks is to prevent a monster from attacking something too strong and getting hurt in retaliation, and if the attacker’s modus operandi is to blow itself up at the enemy, that isn’t relevant.
Exploding pets should not count against you when you kill them. (Not stated if this should apply only to pets which explode upon death, or it should apply to pets that explode even not upon death.
Noxious sphere, a sphere similar to its siblings in that it has an active explosion attack, but the explosion is of poison and creates a 3x3 (or larger) stinking cloud centered on the sphere.
If a digesting engulfer eats an e monster that explodes (either actively or upon death) or potentially any monster with an explosion attack, the monster is assumed to explode inside the engulfer, who takes double damage from that attack (or 8 times damage, if the explosion is considered to have hit them 8 times) and is stunned and immobilized for a few turns, unless they resisted the explosion’s damage type in which case they only suffer that for 1 turn.
This should also extend to other explosions inside engulfers (most of these would be player-created: e.g. reading a scroll of fire or breaking a wand while engulfed).
If polymorphed into a voluntarily exploding monster (e.g. a sphere or light), the player can #monster to explode without actually attacking anything. (You can already do this by forcefighting thin air, so this would just add an additional way to do it and a prompt when you polyself.)
Rainbow sphere, a monster that appears and behaves as if it were any other type of sphere with an exploding attack, but it does not die when it explodes; it becomes a different, random sphere type. There are two possibilities for how it can be killed: it could be brought down to 0 HP like normal, or it could have a limited number of incarnations, after the last of which it explodes and dies normally.
Internally, it should use newcham to handle its transformations; possibly it could be implemeted as a shapechanger capable of turning into any explodable e monster.
Add a new type of eye with a hallucination-inducing active gaze attack. It could be called either “third eye” or “pseyechedelic”.
All spheres should explode in a 3x3 explosion like gas spores do. They should do this regardless of whether they died by attacking or some other method, so they should have an appropriate AT_BOOM attack.
Add spheres that give buff effects and deal no damage to whatever they explode at. They target tame monsters if tame, and hostile monsters if hostile. There is a spell that summons them.
If monsters with area-of-effect passive attacks are implemented, these monsters should perhaps be eyes instead of spheres, and have the buff effect as their passive, and no explosion attack.
Add stunning and confusion spheres, which cause those effects when they explode.
Sphere conjurer: a monster who creates hostile spheres.
