Urzas Cave Busted in Commander, Urza's Cave seems tempting in some kind of The Enigma Jewel deck, which is barely fringe in Standard, much less Modern
Most Commander decks are going to want the vast majority of the remaining cards to be creatures, but if youre playing a deck that only cares about a different type of card, say instants or enchantments, then youll likely want to finish the deck off with those instead

The format looks substantially different and continues to forge into new territory: Selesnya Company $778 [MTGO: 218 Tix][MTGA: 15 Mythic, 46 Rare, 2 Uncommon, 12 Common] Golgari Midrange: $765 [MTGO: 199 Tix][MTGA: 14 Mythic, 39 Rare, 13 Uncommon, 9 Common] Sultai Scapeshift: $729 [MTGO: 151 Tix][MTGA: 10 Mythic, 39 Rare, 15 Uncommon, 11 Common] Rakdos Midrange $689 [MTGO: 60 Tix][MTGA: 11 Mythic, 41 Rare, 12 Uncommon, 11 Common] Niv to Light: $534 [MTGO: 36 Tix][MTGA: 21 Mythic, 57 Rare, 12 Uncommon, 5 Common] Abzan Greasefang $403 [MTGO: 78 Tix][MTGA: 9 Mythic, 43 Rare, 10 Uncommon, 13 Common] Hidden Strings $383 [MTGO: 97 Tix][MTGA: 8 Mythic, 41 Rare, 18 Uncommon, 9 Common] Azorius Control $366 [MTGO: 77 Tix][MTGA: 11 Mythic, 48 Rare, 13 Uncommon, 4 Common] Jund Sacrifice: $280 [MTGO: 55 Tix][MTGA: 10 Mythic, 29 Rare, 27 Uncommon, 9 Common] Izzet Phoenix $207 [MTGO: 157 Tix][MTGA: 7 Mythic, 27 Rare, 16 Uncommon, 25 Common] Its important to note that Pioneer is available on Arena

Neither of these records are going to be easy to beat (with a shorter probably being impossible)
The cards that didn't get put on the bottom of their owners' libraries will return to the battlefield as Trial of a Time Lord leaves the battlefield