Land's Edge

Discard a card: If the discarded card was a land card, Land's Edge deals 2 damage to target player or planeswalker. Any player may activate this ability.

Chronicles Foreign Black Border

Chronicles

Any player may choose and discard a card from his or her hand at any time. If a player discards a land, Land's Edge deals 2 damage to target player of that player's choice.

Legends

Any player may discard a card from hand at any time. If that player discards a land, Land's Edge does 2 damage to target player of the discarding player's choice.

The damage done when you discard a land only applies to lands which are discarded by choice using the Land's Edge ability. It does not work on forced discards of any type.

This has the supertype world. When a world permanent enters, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter at the same time, they're both put into their owners' graveyards.