Leyline of the Guildpact

A player's "opening hand" is the hand of cards the player has after all players have taken mulligans. If players have any cards in hand that allow actions to be taken with them from a player's opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.

Giving a land additional basic land types doesn't change its name or whether it's legendary or basic.

Each land you control will have the land types Plains, Island, Swamp, Mountain, and Forest. They'll also have the mana ability of each basic land type (for example, Forests have " tap : Add green mana ."). They'll still have their other subtypes and abilities.