Wow, I think the mechanics here are really well polished. Aesthetics are on point. The level design and pacing as you introduce each mechanic is really great as well. I think my only critique is it feels a bit loosely tied to the theme. I don't find myself wondering what any of the buttons do, I just have to collect the runes to unlock "standard" 2d platformer controls that are self-evident by the rune icons.
The game feels like it could have fit in with GMTK's 2020 Game Jam. In his recap video, Mark Brown even talks about a theme in some submissions where the controls are represented as in game entities @ ~3:49,
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Thanks for playing! I agree with your critique, in hindsight I think the only times you would ask "what does this button do" is right after collecting the rune; then you know, so there's not much more to it than that. Maybe an interesting spin could've been having separate levels where the rune maps to a completely different action in each level (i.e. the left rune now makes you jump in another level), so you have to keep guessing.
Great point about the GMTK game jam correlation, I didn't think about it at the time but this game definitely borrows that idea about controls being part of the game world. I thought that was a cool application of the theme in that game jam, so I'd love to explore this idea more when I get the chance!