Creatures (20) 4 Eidolon of the Great Revel 4 Monastery Swiftspear 4 Bomat Courier 4 Hazoret the Fervent 4 Rampaging Ferocidon Lands (21) Spells (19) I built this list to be as big as possible in order to accommodate Rampaging Ferocidon, which is an appealing card in the early days of the format since it helps combat the Felidar Guardian combo decks
Dont discount the fact Wayfarers Bauble is an artifact
Not every opening hand will look like this, but I would be hesitant to keep a hand without a one-drop creature, especially in pre-board games
3 Arceus LV
While Atraxa sits outside of Umbris's color identity and cannot fit within an Umbris Commander deck, its sheer power and potential lands it on this list
While 0/1 tokens may not seem like much at first, thanks to its Landfall ability, whenever a land enters the battlefield under its owner's control, that player puts a +1/+1 counter on each plant they control, meaning these tokens can become threatening very quickly