Corrupt - Despicable - Execrable
Don John's motivation is to make everyone as misrable as he is. He envies yet despises Claudio and Hero's marriage because it is something he will likely never get, therefore in his mind, no one else should be able to either. Because of this, he confides in Borachio, "Any bar, any cross, any impediment will be med'cinable to me. I am sick in displeasure to [Claudio]...How canst thou cross this marriage?"
Don John is Don Pedro's bastard brother, so nobody respects him. He knows this, and tells Conrade, "If I had my mouth, I would bite; if I had my liberty, I would do my liking. In the meantime, let me be that I am, and seek not to alter me." Don John convinces himself that there is nothing he can do to change things. In this way, he is a very reactive person, and simply accepts his fate to be unwanted and unloved. Because he doesn't try to change himself, he doesn't end up changing or being developed as a character.
Don John impacts the plot by creating the conflict. Without him, Claudio would have no reason to doubt Hero, and they would have been married as planned. He is the sole reason there is a play at all. Don John doesn't seem to love anything except chaos and possibly himself. Therefore, he has ludos love because chaos is crazy and unpredictable; the only way to love chaos is to treat it like a game.