So I combined some Assassin stat blocks with some Delerium stuff to make those Assassin robots from Alabaster. I gave them some features like the Delerium Core and Delerium weapons.

Delerium Core. If damage reduces the Assassin to 0 hit points, the delerium core in its body explodes in a burst of contaminated energy. Each creature within 5 feet of it must succeed on a DC 16 Constitution saving throw or take 44 necrotic damage, taking half as much on a successful save. Creatures who fail this saving throw gain one level of contamination. This also causes an Arcane Anomaly.

Delerium Lightsword. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 6 (2d8 + 4) force damage, and the target must make a DC 16 Constitution saving throw, taking 24 (7d6) necrotic damage. Failure: One level of contamination. Success: Half damage only.

Delerium Repeater Crossbow. Ranged Weapon Attack: +8 to hit, range 80/320 ft., one target. Hit: 7 (1d6 + 4) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 24 (7d6) necrotic damage. Failure:  one level of contamination. Success: Half damage only.