Abner Cadaver is Rottytops and Poe's brother. Though rough around the edges, Abner is a devoted older brother who cares deeply about his siblings; he chides Rottytops for her pathological inability to stay out of trouble, and works hard with Poe to keep his family sane without having to eat the brains of those in Sequin Land.
The brothers do not appear in the original game, but they are mentioned fearfully by other zombies at the Zombie Caravan. Shantae is told that she is fortunate that they are not around because they are a lot of trouble.
In Risky's Revenge, Abner Cadaver and Poe appear together three times. First, they are waiting for Shantae at the exit of a Tangled Forest Cave where the Elephant Magic Fountain is located. They strike a deal with her: providing her with a tool to get in Hypno Tower in exchange for coffee with a rotten egg (as they inform her that coffee is the only thing preventing zombies such as them to become mindless). Shantae meets them for the second time at the Boat House, where she exchanges coffee for what happens to be explosives to blow up the grid at the Tower's entrance. They appear one last time alongside Rottytops in Risky's Lair near the end of the game, having abducted Mimic in exchange for a lifetime supply of coffee (and in the case of Rotty, for Shantae's brains). However, Risky backs down from the deal, and the trio is last seen bitterly leaving the Lair, just as Shantae arrives.
In The Pirate's Curse, Abner returns, living with Poe and Rotty on Spiderweb Island. After Rottytops tricks Shantae into carrying her home, Abner apologizes to Shantae for his involvement with Risky and Shantae's subsequent loss of her abilities, saying that Risky "has a way of getting in your head and telling you what you want to hear." This immediately strikes a chord with Shantae, who remembers full well Risky's own actions in the first Shantae game. He thanks her for being nice to Rotty, in spite of Rotty's trickery, and informs her that he's got her back if she needs help.
During Shantae's trek through Mud Bog Island, talking to Abner reveals that the Village of Lost Souls "don't sit well with [him]", perhaps because of his zombie nature. Much later, after Shantae returns from the island, Shantae has Rottytops identify the Lost Soul of Barracuda Joe. When asked where she got it, Shantae almost talks about the Village of Lost Souls, but Abner encourages her not to - seeming to know more about it than Shantae herself does. Shantae defers to Abner's request, disarming Rotty's questions about the village and earning the gratitude of Abner in the process. He also offers to take Shantae's now-useless Death Mask off her hands in return for a Pirate Flare.
At the end, it is revealed that the zombies have moved back to the mainland. After leaving Rottytops in care of Shantae at Shantae's Lighthouse, Poe and Abner Cadaver leave together in search of their former identity, and also of the Zombie Caravan, which they plan to re-join.
In Shantae: Half-Genie Hero Abner appears in Hypno Baron's Castle and contemplates on adding a poster to the Castle that he soon plans on taking over with Poe. After Shantae receives the Velvet Poster from the Squid Baron and gives it to Abner he is delighted at how the poster looks and gives Shantae a Squid Poster. Abner claims that Poe picked it up at a "nerd-con", and only gives it to Shantae because he wanted to get rid of it.