Since I ended up with only 160 cards from my original rules-based methodology, I'm adding into the Maybeboard all cards that were first printed in Time Spiral and Planar Chaos and not reprinted during the pre-F.I.R.E. era of Standard, as well as cards first printed in Dominaria United, Brother's War, and their respective Commander sets, given that those obviously wouldn't have been able to be reprinted earlier. From these, I can pull remaining archetype support/payoffs or staples.

I believe Defender is an essential part of Magic, so I included all those Walls. Also--notwithstanding DMU's Green + good stuff multicolor piles Limited--I pulled all the Lands I could.

I wish I could've included all those Slivers, as that's one of my favorite archetypes in all of Magic, but I had to cut them to get down to 184.

Added cards from DMU and BRO that were rebalanced on Magic: Arena.

And added to Maybeboard cards from Alchemy: Dominaria United and Alchemy: Brother's War that I think could work in a Bar Cube with 3+ players if at least 1 of the players not in the 1v1 in question is willing to look through a player's deck (for seek); otherwise, a player can just set aside a card in their hand to indicate it is the one that they chose to give a perpetual effect to (and then it's up to both players to remember all perpetual effects for the rest of the game).

All the non-Rare cards that were printed during the pre-F.I.R.E. era of lower-powered design for Standard (BFZ-M19) that were also printed in a Dominaria/Weatherlight Saga set before or after (the printing that I would use).

After Derek Gallen, there are no tokens, counters, or dice-matters effects.

And after Zac Hill, there are no card-draw or ramp effects, nor creatures with base power or toughness greater than 5 with a casting cost less than 4, nor unconditional removal with a casting cost less than 3. (Accordingly, I've left out any cost-reducers.)

And after Sam Black, there are no tutors nor cards that cost 2 or less that can tap for 2 or more.