Creepy Jack

Creepy Jack is a halloween-themed trinket that summons a pet.

Source
The item can be purchased in East End Police Station (heroes) or The Gotham Tap Room (villains) during The Witching Hour event.

Deep Sea Chanter
Upon activating the trinket, Creepy Jack is summoned to aid the player in battle. Creepy Jack will heal its controller once the player's health drops below 40%.

Attacks:

 * Ball - does a single attack for 40 damage (on training dummy).
 * Beam - does four consecutive attacks, each for 14 damage (on training dummy).