what does it mean to cast play eldrazi from outside the game

[Swishhh]

am talking about this card:

Spawnsire of Ulamog

what does it mean casting a eldrazi card from outside the game

[Arix]

Exactly what it says. You choose any number of Eldrazi cards you own from outside the game - that is, any that didn't begin the game in your deck - and cast them.

[Kenji]

It should also be noted that "outside the game" in a sanctioned tournament refers to your sideboard only. So, in a tournament, 15 Eldrazi is the most you'll ever be able to cast via Spawnsire (and that's assuming your entire 15-card sideboard is Eldrazi cards).

Of course, in casual play, it has the literal meaning of any card that didn't start the game in your library. It doesn't let you cast exiled Eldrazi, because exiled cards go to the exiled zone, which is not outside of the game.