Witchstalker

A 3/3 hexproof body for three mana is a clean rate on its own; the second ability is a deliberate piece of color-pie warfare. The growth trigger fires only when an opponent casts a blue or black spell, and only during your turn, which is a precise way of saying: this creature is built to feed on the instant-speed interaction that control decks live on. Hexproof already locks out targeted removal, so a control opponent cannot simply point a kill spell or a bounce spell at it. What remains is the reactive blue and black they cast on your turn anyway: a counterspell aimed at your other threats, an instant-speed draw spell to find an answer, a combat trick during your attack. Each of those, cast in your turn, ticks the wolf up another notch. The window is the whole design. By restricting the trigger to your turn, the card ignores the proactive spells an opponent plays on their own turn to develop a board or refill a hand, and cares only about the answers thrown at you. It is a beater reverse-engineered from its worst matchups: the decks that most want to grind down a resilient green threat are the decks whose own reactive spells make it bigger. Against aggro or other green decks the counter ability simply lies dormant and the wolf attacks as a removal-proof 3/3, the honest cost of a payoff written partly in the enemy's colors.