I don't mind either way,  as long as those working on the game are cool with it. Don't want an easter egg causing any extra stress!

It doesn't matter how well-meaning a person is in the use of generative AI, since there are several enormous caveats to consider in using it at all; Namely, image generators have to be trained using the work of actual artists, only to produce cheap imitations with no actual human thought or effort behind them. It's a downright insult in the case of fan art, because the sum of YOUR work is being soullessly blended and bastardized for something the "fan" "artist" did not make, only to be handed back to you in YOUR honor.
Additionally, while the energy cost of producing a single image might not raise any eyebrows, but continual use of image generation models snowballs into a massive environmental impact (typically since AI users will continually iterate and re-generate outputs to achieve a desired result) and this in turn also incentivizes the creation of more AI datacenters, which are an incredible drain on local power grids and water supplies.

Put simply, there is no artistic, moral or practical argument to be made for allowing it at all.

AI art is not art, if they really respected the project they'd put in the effort to pick up a pencil and learn how to draw

AI art isn't fanart, it's just an insult to fans who have made art; and artists working on the actual game

I gotta be a hater here about the AI stuff. I'm unsure how to word it, it feels insulting to the artist and the artists past and future who draw Mall Creeps to include it. No issue with people making it but to include it in the game is another thing entirely.