Toph, the First Metalbender

The land will retain any other types, subtypes, or supertypes it previously had. It will also retain any mana abilities it had as a result of those subtypes. For example, a Forest that's turned into a creature this way can still be tapped for {G}.

"Earthbend N" means "Target land you control becomes a 0/0 land creature with haste in addition to its other types. Put N +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped under your control."

If a land was animated by earthbend and would go to any zone other than the graveyard or exile, it will not be returned to the battlefield by the delayed triggered ability created by earthbend.

If the targeted land becomes an illegal target before the spell or ability that includes earthbend resolves, earthbend does nothing. If the spell or ability didn't have other targets, it won't resolve.

You may target a land that is already a creature, perhaps because of a previous earthbend ability. The land will get the +1/+1 counters, gain haste, and have its base power and toughness set to 0/0.

Toph, the First Metalbender's first ability does not allow you to play nontoken artifacts as lands. It only affects permanents on the battlefield.

Earthbend doesn't give the land you control a color. As most lands are colorless, in most cases the resulting land creature will also be colorless.