Lightning Greaves
ETBs here are as close to guaranteed wins as investing gets
Say you want access to Lurrus of the Dream-Den, Yoshimaru, Ever Faithful, and Miara, Thorn of the Glade, you can meet all the requirements for Lurrus, and partner the dog and the scout, but just because it can be done doesn't mean it should be
This box holds up to 120 sleeved cards or 110 double-sleeved cards , making it perfectly sized for Commander decks
While Black Panther can spread counters, so can other cards, so you don't have to rely only on Black Panther for your +1/+1 counter needs
There are lots of other lands I could mention, like Brian Snoddy's take on Urza's Power Plant, John Avon's Lantern-lit Graveyard and Submerged Boneyard by Chris Childs, and many others