i brought them there at the same time and went to the shrine and pressed ''a''.......wheres landorus
Like UberPwnage said in his comment, you need to bring them to Abundunt Shrine at the same time. They both need to be in your party for this to work.
>Landorus, the embodiment of fertility, can be battled here if Tornadus and Thundurus are in the player's party and one of them is originally from the player's game. -Bulbapedia
Hope This Helped :D