Search your library for a green creature card with converted mana cost X or less, put it onto the battlefield, then shuffle your library. Shuffle Green Sun's Zenith into its owner's library.
In most cases, if you own Green Sunâ€™s Zenith and cast it, youâ€™ll shuffle your library twice. In practice, shuffling once is sufficient, but effects that care about you shuffling your library (like Psychogenic Probe, for example) will see that youâ€™ve shuffled twice.
If you own Green Sunâ€™s Zenith, but an opponent casts it (due to Knowledge Poolâ€™s effect, for example), that opponent searches their library for an appropriate creature card, then shuffles that library. That opponent then shuffles Green Sunâ€™s Zenith into your library. You wonâ€™t shuffle any library in this case.
If Green Sunâ€™s Zenith is countered, none of its effects will happen. Notably, it will be put into its ownerâ€™s graveyard rather than shuffled into its ownerâ€™s library.
If this spell doesnâ€™t resolve, none of its effects occur. In particular, it will go to the graveyard rather than to its ownerâ€™s library.
BUY THIS CARD