Xander, Scion of Mirstone

You may pay {w}{u}{b}{r}{g} rather than pay the
mana cost for the spell that you cast.

{7}: If you both own and control Xander Grey,
Scion of Mirstone and an artifact named The Shard,
exile them, then meld them into Xander, Herald of
the Ravenous Void. Activate only as a sorcery.

What are those of the known, but to ascend and enter
the Unknown?