The inspiration for the character of Sqij being a mutant bird came from Jeff Minter, known for his ruminant-themed video games. Sqij! creator Jason Kendall would say to Eurogamer in 2017:

The mutant bird illustration on the box art for Sqij! and Obitus, drawn by speculative fiction artist Tim White, seems to have originated from the 1979 edition of the 1975 book Under a Calculating Star. It is unknown if either use was licensed.

The ZX Spectrum version of Sqij was made using Ocean Software's Laser BASIC coding software, and contains significant chunks of the library in its code, which could be easily reverse engineered, allowing one access to the suite of Laser BASIC tools for the £1.99 price of Sqij as opposed to the £14.95 asking price of Laser BASIC.

The ZX Spectrum release of Sqij! has been cited as one of the worst games ever made, sometimes even being referred to as the single worst video game ever made, due to a bug that renders Sqij uncontrollable unless the game is modified with the POKE button (a button on the ZX Spectrum that allowed users to modify code of software, somewhat like a built-in Game Genie). The conversion was handled by a 15-year-old named Jason Creighton, who intentionally created a lackluster version of the game expecting it to be rejected, in protest against being mistreated during development, with a particular point of contention being that he wasn't provided with the original Commodore 64 version of Sqij! to study. However, the infamous bug that rendered the game unplayable was not an intentional inclusion.