Nurse Mouth was added in Beta 30.0. Previous Versions can be found here.
Nurse Mouth, as Big Mouth's Deltarune counterpart, is also a Rare and has the exact same stats of 3/6 for 5G.
Its ability allows it to let you restore 3 HP whenever an ally monster dies if it costs 3 or more. This can be used very well alongside most Taunt monsters, as they will protect Nurse Mouth while also being able to heal you up when it dies. Keep in mind that Nurse Mouth will NOT trigger when it dies itself, similar to Loren.