* Forgiveness and generosity: The antonym could be pettiness, vindictiveness, or spitefulness.
* Nobility and greatness of spirit: The antonym could be meanness, selfishness, or small-mindedness.
* Forbearance and mercy: The antonym could be cruelty, ruthlessness, or unforgiveness.
Ultimately, the best antonym for magnanimity will depend on the specific context in which you're using the word.