The +2/+0 buff is useful because there are many scenes where multiple mice are lined up, and you can trigger Valiant simultaneously, or use it on two [Diverse Mice] created with offspring to deal 12 damage
Since you will likely be attacking with a lot of creatures, it turns any of them into potentially game-ending threats as well as deterring the opponents from attacking into you or risk losing their creatures
Gotta play 'em all
Of course, if you don't have these cards or even anything close to them, it's worth considering the Lt
Sets that primarily take place there : Innistrad , Dark Ascension , Avacyn Restored , Shadows over Innistrad , Eldritch Moon , Innistrad: Midnight Hunt , and Innistrad: Crimson Vow Planeswalker natives (with planeswalker cards) : Arlinn, Sorin, and Tibalt Innistrad is a plane inspired by the horror genre, especially the subset of gothic horror