@ronaldo (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1227) brought up this demo in ESP back in 2015 after shao asked what could be done in BASIC and I couldn't find anything about it on this Forum! :( I thought it was rather cool. It has some bugs in it and it's not 464 friendly (to do with the Multicoloured Graphics and String management), though here's a link to the site (in Spanish) (http://fremos.cheesetea.com/download/gortmy-demo-tecnica-2014/).
A translation in English Read's as:
QuoteEscape from Gortmy planet is a game concept created for the 2014 Retroaction BASIC programming contest. It is a simple game concept (scrolling top view matamata), but with a significant technical development. A number of optimization ideas are included in BASIC, such as encoding the maps in compressed binary and reserving a memory area for them, or using byte vectors accessed by hand via POKE / PEEK. Likewise, a scroll map system is implemented taking advantage of the system's hardware capabilities, and an enemy spawn system.
All this was developed in 48 hours, leaving this development version (technical demo) in which you can see some of these characteristics and understand how it works.
Oh and the controls used are W,A,S,D, your contraption also fires, though couldn't figure if it was 'f' or something else.