Homebrew
Death Burst. When the mera dies, it explodes in a burst of elemental ice. Each creature within 5 feet of it must make a DC 10 Dexterity saving throw, taking 4 (1d8) cold damage on a failed save, or half as much damage on a successful one. Extinguished. Upon taking fire damage, the mera must succeed on a DC 10 Constitution saving throw or fall prone, the elemental energy within it having been extinguished. False Appearance. While the mephit remains motionless, it is indistinguishable from ordinary ice.
Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 3 (1d4 + 1) bludgeoning damage plus 2 (1d4) cold damage. Frost Breath (Recharge 6). The mera exhales a 15-foot cone of cold air. Each creature in that area must succeed on a DC 10 Dexterity saving throw, taking 5 (2d4) cold damage on a failed save, or half as much damage on a successful one.