You can activate the ability multiple times targeting the same land to add more counters
If you control another player's commander, you won't create a Mercenary when you attack with that creature
Cards that are officially spoiled so far can be found here
Aboleth Spawn Abstruse Archaic Adric, Mathematical Genius Ancient Greenwarden Annie Joins Up Annie Joins Up Brokers Confluence Clara Oswald Cloud, Midgar Mercenary Consign to Memory Defabricate Delney, Streetwise Lookout Deny the Witch Detect Intrusion Disallow Drivnod, Carnage Dominus Echo, Perceptive Prodigy Echoes of Eternity Elesh Norn, Mother of Machines Emerald Dragon Emerald Dragon Ertai Resurrected Felix Five-Boots Firebender Ascension Gandalf the White Gogo, Master of Mimicry Green Slime Harmonic Prodigy Isshin, Two Heavens as One Isshin, Two Heavens as One Katara, the Fearless Kirol, Attentive First-Year Krang, the All-Powerful Lithoform Engine Louisoix's Sacrifice Mirror Room // Fractured Realm Mirror Room // Fractured Realm Mister Fantastic Naban, Dean of Iteration Nimble Obstructionist Overcharged Amalgam Panharmonicon Panoptic Projektor Peter Parker's Camera Phenomena Recorder Repudiate // Replicate Repudiate // Replicate Return the Favor Roaming Throne Roaming Throne Sanctum of All Scientist Supreme of A.I.M
