That could be an opponents creature, planeswalker, or even their life total directly
That is, lands as a mechanic in general
Barad-dr The ability on Barad-dr isnt efficient, but its borderline free to slot into your mana base
Assaultron Dominator Big Mother Mouser Celebr-8000 Chrome Dome Codsworth, Handy Helper Curie, Emergent Intelligence Depthshaker Titan Dragon Man, Reformed Robot ED-E, Lonesome Eyebot Emissary Escort H.E.R.B.I.E., Lovable Robot Jocasta, Automaton Avenger K-9, Mark I Krang, the All-Powerful Mendicant Core, Guidelight Mister Gutsy Omniclown Colossus Panther Robot Patrolling Peacemaker Pinnacle Emissary Ravenous Robots Repulsor Bots Rex, Cyber-Hound Roadkill Rodney Rose, Cutthroat Raider Rust Harvester Securitron Squadron Sentry Bot Super-Adaptoid Surge Conductor The Motherlode, Excavator The Vision Tri-Sentinel, Act of Vengeance Ultron, Machine Overlord Ultron, Unlimited Vision, Spectral Synthezoid Vision, Synthezoid Avenger Yes Man, Personal Securitron
Some effects, like Dingus Egg, can pay you off when a land goes to a graveyard