🗿 notawikiAcross the Obelisk Codex · the answer, not the article

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Batsy
pet  Pets · Unlockable pets
Slashing, Piercing resistance +6%. [Every turn] Cast card Echolocation.

🃏 Its card: Echolocation

Apply 4 Insane, 4 Mark.

Corrupted (purple) version
Max HP +5. Slashing, Piercing resistance +8%. [Every turn] Cast card Echolocation [Corrupted].

🔑 How to unlock Batsy

Unlocked in the Forge in Act 4, the Castle Grounds.