Osgir, the Reconstructor | Ugin's Nexus | Mirror of Fate

(and one other card)

Activate
Osgir's second ability by paying ({5} magic symbol) , tapping it and exiling
Ugin's Nexus from your graveyard, creating two token copies of
Ugin's Nexus.
Exile one of the
Ugin's Nexus copies due to the legend rule, causing you to take an extra turn after this one.
Activate
Osgir's first ability by paying ({1} magic symbol) and sacrificing the remaining
Ugin's Nexus token.
The
Ugin's Nexus token is exiled instead of being put into your graveyard, causing you to take an extra turn after this one.
Resolve the
Osgir ability, giving a creature you control +2/+0 until end of turn.
Move to your first extra turn.
If you do not control a
Mirror of Fate token, activate
Osgir's second ability by paying ({5} magic symbol) , tapping it and exiling
Mirror of Fate from your graveyard, creating two token copies of
Mirror of Fate.
Activate a
Mirror of Fate token by tapping and sacrificing it, choosing
Ugin's Nexus, any other card in exile,
Mirror of Fate and up to four other cards in exile, then exiling your library and putting the chosen cards on top in the aforementioned order.
Activate
Codex Shredder's first ability by tapping it, causing you to mill
Ugin's Nexus.
Move to your second extra turn.
Activate
Codex Shredder's first ability by tapping it, causing you to mill
Mirror of Fate.
Repeat.