Sensei Golden-Tail is a rare Legendary Creature — Fox Samurai card from Champions of Kamigawa (CHK), collector number 44. Current market price: $1.73 (foil $10.82), TCGplayer market prices via Scryfall.
Bushido 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.) {1}{W}, {T}: Put a training counter on target creature. That creature gains bushido 1 and becomes a Samurai in addition to its other creature types. Activate only as a sorcery.