For more information on the Cubelet format, refer to episodes 39 and 40 of LoadingReadyRun’s Tap Tap Concede podcast.
Cards primarily get added to this cubelet from cards opened during pack wars following the release of new Standard-legal sets. I started playing Magic around Amonkhet, so the bulk of my collection comes from Frontier-legal sets (sets using the M15 card border released into Standard), making it a nice restriction for this cubelet build.
The goal is to have a stack of 100 cards and a few dice I can carry around with me to get a quick casual game of Magic at any time, with pet cards and cards otherwise unplayable in constructed formats I’m interested in.