Multi Shot brings back the old version of Shootout in a better form. Whereas one Shootout turned the passive into: "At the end of your turn, deal 2 damage to a random enemy monster." One Multi Shot turns the passive into: "At the end of your turn, deal 2 damage randomly split among all enemy monsters."
Just two of these cards will make your passive instantly kill a lone Sans.
While this is an upgrade in most situations, monsters with Armor block this version completely. But it's a minor price to pay.
The effect of this card lasts forever, so it's a very good card to have.