Hi, nice concept. I was able to run it fine even with my old ruby, I just needed to convert those fancy one-line definitions without "end"s to common three-liners with "end" in the end.
It took me a bit to realize Concentration is not going to do much but contemplate the current situation. In few cases I was not fully sure whether jumping will get me to miss the upcoming spikes or not, I guess with some more levels it would be an easy-to-be-learned skill. Audio is fine, nice calming colour palette. That help screen with instructions looks really good.
If you are going to add some more cards, consider ones that enable you to switch gravity from down to up so that you can walk on bottoms of platforms (where there may be some more spikes to deal with).