Sparrow, Arcane Guardian

Partner with Fox, Arcane Guardian.
Sparrow, Arcane Trickster can't be blocked.
Whenever you cast an instant or sorcery with converted mana cost 4 or less, you may draw a
card, then discard a card. If an instant or sorcery
is discarded this way, Sparrow, Arcane Trickster
deals damage equal to the discarded spell's mana
cost among any number of target creatures or planeswalkers.