Landfall abilities on your artifacts, creatures, and enchantments do something when a land enters the battlefield under your control. For example, Steppe Lynx says “Landfall — Whenever a land enters the battlefield under your control, Steppe Lynx gets +2/+2 until end of turn.”
Landfall doesn’t care how a land enters the battlefield, as long as it does so under your control. That means each landfall ability on your permanents will trigger whenever you play a land normally, as well as whenever you put a land onto the battlefield as a result of an effect like Rampant Growth. If you do both during the same turn, for example, Steppe Lynx will wind up getting +4/+4! Landfall only cares about your own lands, however—if a land enters the battlefield under another player’s control, your landfall abilities won’t do anything.
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