Slyzards are fire-breathing draconids, often mistaken for dragons though much smaller and less dangerous. The exception is a female in mating season, or one guarding her eggs. The Slyzard Matriarch in Toussaint is exactly that, and one of the most dangerous draconids in Blood and Wine.
Combat strategy
Use Draconid oil and Grapeshot. Quen absorbs her fire and tail blows, and Aard helps bring her down when she lands. Beware her sonic blast, which knocks you to the ground.