What it does
Swampwalk is an evasion ability: a creature with swampwalk can't be blocked as long as the defending player controls a Swamp. It only checks for the land type "Swamp," not the color black, so any land with the Swamp type—including dual lands and basics—triggers it.
The common mistake is thinking the controlling player's lands matter. Only the defending player's lands count, and they just need one Swamp anywhere on their battlefield; the swampwalk creature deals damage unblocked. Note that swampwalk doesn't make the creature "unblockable" outright—if that opponent has no Swamp, it can be blocked normally.
In Commander, landwalk is unreliable because the multiplayer field is full of varied lands. Against three opponents, only those running Swamps are vulnerable, so swampwalk is situational. It shines best alongside effects that give opponents Swamps (like forcing a basic Swamp onto their battlefield) to guarantee the evasion.













