Several other cards that take full advantage of Salvation Engines abilities, including Stridehangar Automaton, Sai, Master Thopterist, and Urza, Prince of Kroog
As long as neither player is manipulating their library or using their graveyard, using a Millstone does nothing but reveal information until the player being milled runs out of cards, but it took more explanation than you can possibly imagine to make players understand this
Putting the burden counters on the player might have done it
Format Legality There are very slight format legality differences between SPM and OM1, specifically because OM1 is legal in Arenas digital-only formats, including Brawl and Timeless
The only issue with this deck is that it doesnt have a ton of cards that are still competitively viable today (with a few notable exceptions like Lefou Instigator and Shield of Virtue)