Flowey / Asriel

Flowey's petals are black and his stem is grey. Flowey is capable of transforming any time. Though Flowey would not remember becoming Asriel, he would still recognize Chara. Flowey does not try to kill you in the start and he would actually be your companion through out the game. If he actually dies, Asriel's soul would be absorbed by you. Once you do you would get green armor and a flower crown with Flowey's head on it. Also through out the game Flowey would mentor you from the crown. So it is advisable to let him die.