Activate "Shien's Spy" or "Creature Swap" to give this card to your opponent, and attack it with "Rose Tentacles". Since "Rose Tentacles" can attack multiple times (depending on the number of Plant-type monsters your opponent controls), after "Horseytail" is destroyed in battle, attack the Horseytail Token with "Rose Tentacles". Your opponent will lose 600 LP (from "Rose Tentacles") and one card from their hand due to the effect of Horseytail Token.
Use "Spirit Barrier" and attack you opponent's stronger monster with this card. Then destroy the "Horseytail Token" with a Plant-Type monster. A "Seed Cannon" card already in play can inflict 1000 damage to the opponent in total.