It follows the adventures and misadventures of the titular initially six-year-old Erma Williams' experiences as a half-human, half-yōkai/ghost, tending to use her haunting abilities for everyday antics, whether for better or for worse, focusing on themes such as friendship and acceptance.

[1] In January 2020, Comics Beat reported that with 64.5 million views and 74.9 thousand subscribers, Erma was the most-viewed webcomic on the Tapas syndicate in 2019.

Santiago also focuses on Erma's supernatural life and friendships with her best friends, Amy, Terry and Connor, as well as her babysitter Felicia and fellow Warrior Unicorn Princess fan Sidney.

Tales of the Outcast is an anthology series that focuses on other notable characters from Erma's world in small side stores.

A third collection, Tales of Outcast, featuring the writing of Donovan Tracy and art of Erik Lervold and Kirsten Celander, was released in 2019.

Beckoning her to him to go home, Erma turns her head, revealing her normal pale face and inverted-coloured eyes.

[7] Santiago revealed that he had a "secret" project in development in addition to Erma #3 in October 2017, which he cited as the reason "there [wouldn't] be as many Halloween strips this month as last year".

[11] Promotional art for the game features Mario encountering Erma as he's about to enter a Warp Pipe, shocked by her appearance.

Santiago has stated that the game was specifically designed for readers of the Erma webcomic, as compensation for a temporary delay in the release of the following strip that existed at the time.

[14] In a follow-up review to that of Miska's for Bloody Disgusting, Jonathan Barkan described Erma as "adorable" and "innocent", expressing fondness the series' "squeal-inducing" moments and citing "Movie Night"[15] as his favourite strip.

[16] Giallo Julian of Dread Central praised Erma as "just wholesome, feel-good content dipped in a nice coating of horror imagery… and you can bet your bloody guts that [one would] love every single bit of it.

It's a celebration of the horror culture in the style of an old Peanuts comic strip", in particular praising its evolution from "one-shot stories establishing Erma [to] longer narratives, and [how] it begins to flesh out a creative world that [is] just a joy to see".