What it does
Plainswalk is a form of landwalk: a creature with plainswalk can't be blocked as long as the defending player controls a Plains. It's evasion, plain and simple—if your opponent has the right land type, your creature swings through unblocked.
The most common misunderstanding is what counts as a "Plains." It's the land type, not the name, so any land with the Plains subtype triggers it—including dual lands like Hallowed Fountain or Sacred Foundry, and even nonwhite decks running fetchable Plains-type lands. Also note plainswalk only grants evasion; it does nothing to protect your creature from removal, and it doesn't force the creature to attack.
In Commander, landwalk is unreliable because of the four-player, multicolor environment—plenty of opponents won't run Plains at all. It's situational evasion at best, occasionally backed by effects that give an opponent's lands the Plains type to guarantee it connects.



