Artifact bronze plate mail The Pact Eternal. Autocurses when worn. When invoked, it summons a tame copy of you, with copies of your armor and wielded weapon (which only works on a wielded weapon), drains 1 level from you, and reduces your maximum HP by half.

If you die while the summoned copy lives, you get lifesaved, the max HP penalty becomes permanent, the copy is unsummoned and you are relocated in its place (to produce an overall effect of it becoming the “real” you.)

If you take off the armor, the copy is unsummoned.

If the copy dies or gets unsummoned by any means, its gear vanishes along with it, and your missing max HP is restored (though your current HP does not get restored).

Lava gremlins: a different gremlin species that reproduces in lava instead of water. It has at least one physical damage attack and at least one fire attack, and the regular gremlin intrinsic-stealing attack, except they steal intrinsics during any time that is not night.

A new type of pudding or slime (though possibly a j or b monster) that has a high speed and good attack and splits whenever it takes damage. Its entire strategy is based on surrounding you with lots of clones that all have the same high attack as the original. Has a high monster difficulty; possibly, their attack stats and difficulty should be high enough that they will usually not show up until Gehennom.

This is unintentionally quite similar to Brogue’s fearsome pink jelly.

As a reference to the game Centipede, if you hit a centipede (only with a slashing weapon?) and it still has over 50% health, it has a small chance of splitting into two centipedes. Both monsters are flagged or cancelled so that they cannot split further.

Monsters that divide/split must find a space adjacent to the splitting monster that is safe for the new monster to be on; if no space exists, the split doesn’t happen (and any effects on the monster’s current or maximum HP are nullified).

Currently, the split monster lands on the closest available square, which could be not at all close to the original monster in a packed environment, and this is weird.

Artifact figurine Doppeldoll: when applied turns into a tame clone of yourself with copies of all your weapons and armor.

A digging ray shot into amorphous engulfers (such as green slimes or gelatinous cubes in some variants) splits them instead of reducing their HP to 1. This automatically makes you not engulfed anymore. (Does not change the effect on things like purple worms. Not specified what should happen with unsolid engulfers like vortices and air elementals.)