Option 1:

Hipnoshroom.

They are a shy type of encounter that hides themself in delusions of others. They are a sweet and quite a nice monster that loves hugs, but ruined by everyone that bullies them for their poor magic skill. [Pacifist] try to comfort these fellas and show them that they are enough as they are while showing them that they are very strong. After you do that, you will know when to use mercy when illusions are gone and they have 2 eyes.

Option 2:

Mushroom brothers.

They protect eachother and fight like a unite. They are very nice monsters who love helping others in any way they can. [Pacifist] They are like one, make one feel good and everyone will appreciate you. [Genocide] Cut them one by one from their roots.

Option 3:

Childshroom.

They are a youngling that's proud to be one of the few mushrooms in the grove that have arms. They love to help others with their hands. [Pacifist] they love to play games like catch but they are really bad at them. Try playing some games with them and let them win. [Genocide (optional)] Cut off their arms and win round in 3 attacks instead of 4.

Option 4:

Eldershroom.

He's just an old tanky mushroom. He lived long and quite unhappy life. [Pacifist] try to remind him of his old days when he was happier. Try to act like a little kid and say silly jokes. [Genocide] End him of his misery.

Everyone thank @AkkiKiller508 for these amazing concepts!!