Mooshroom Cow Pet

The Mooshroom Cow is a craftable Pet unlocked at.

Trivia

 * The Mooshroom Cow used to be the best farming pet in the game immediately after its release with the Crimson Isle Update, the reason for that was that its perk Mushroom Eater used to drop one of each mushroom per crop broken (or 2 in the case of sugar cane because you break 2 blocks in one go) and they were affected by Farming Fortune. On top of that, its 3rd ability, Farming Strength, used to be 1 Farming Fortune every 10 Strength instead of the current 20 at level 100.
 * All of that combined, plus the fact that mushrooms have a very good NPC sell price made the Mooshroom Cow pet the best farming pet in the game, players with high strength optimization and high farming levels were able to get up to 10-12m per hour easily.