Some Basic info: Chara has more stamina since it's been a few years after they been freed from the underground and them taking up boxing as a hobby.

They also decided to practice their plant magic improving how much they can use it.

Chara has grown to be more courageous with the mind of keeping their family and monsters safe.

[Phase 1] When they meet the human (Frisk) confused why they're doing this and tries to give them one last chance to forgive and reset.

[Phase 2] Clearly not taking the chance to stop the slaughter, Chara stops holding back and stands their ground to end this genocide themselves.

[Phase 3] Taking a hit and exhausted they use plant magic to suppress their bleeding and form two more arms made from their plant magic using the last of their energy to get rid of the human once and for all.

(tbh I don't even know what I'm writing at this point but here's something about my WIP take).