I present to you some minor, weaker guardians - Companions!
Napstastern: A ghost whose primary ability is "calming". They're power is similar to the "daydreams" Toriel uses to neutralize nightmares or anomalies. Because of this, Stern is generally summoned by all guardians except her. While flying, they showers the ground and creatures beneath them with intangible stars, which create a calming effect.
Lesser Dog: Its summoning is more suited to close combat. It wields a shield and sword, and its special characteristics include incredible speed, thanks to the strength of its canine paws.
Bufohill: Similar to Froggit. Its name is a combination of the constellation Bufo and its discoverer, John Hill. Objectively, one of the weakest Companions, but can temporarily cast a shield on itself and nearby guardians. Its weakness is that the shield lasts only a short time and has some interruptions.
Some interesting facts?
I put some effort into the names of these characters, since, unlike the main cast (exept Aster and Mystic), they have names related to space. I also wanted to come up with something interesting for Lrsser Dog and turn its name into a constellation, but when I went to research it, I discovered that the constellation Lesser Dog (Canis Minor) already exists, so I left it as is.
Also, while designing them, I came up with the emblem for all the guardians. It doesn't matter that only the Lesser Dog actually has it, I still wanted to keep it :).