MTGNexus

Would this work as intended, that is, like landwalk only for world permanents instead of for lands?

Worldwalk (This creature can't be blocked as long as defending player controls a World.)

If it does work, would the reminder text need "permanent" after "World"?

Here is the current rule:



While it is only expecting this to care about lands, it does allow [type] to be any Supertype (and World is a Supertype) so by the current rule "Worldwalk" works just fine. A later rule is more clear on it really just caring about lands so, most likely, the rule would be updated to simply genericize the ability further but I don't see anything exceptionally wrong with the wording as is.

As for the reminder text: you can make that whatever you want. Reminder Text isn't rules text but even your reminder text already implies "permanent" so I wouldn't worry about changing it from a rules perspective.

Supertypes aren't capitalized, so your reminder text implies that you introduce a new subtype called World.