Grottore is a powerful spriggan, a relict related to leshens, found in Toussaint in Blood and Wine. Like other spriggans it controls the forest around it, attacking with magic roots and summoning archespores.
Combat strategy
Use Relict oil and Igni, and throw a Dimeritium bomb to weaken its magic. Destroy the archespores it summons and dodge the roots erupting from the ground.