Saga is arriving to the island after the destruction of the Crying Wall in the underworld; his history can be found here on Wikipedia.
Being the original manga version, please disregard any references to the anime, the canonically-debatable Episode G manga, or the non-canonical Legend of Crimson Youth movie. (Any further disambiguations will be happily cleared up.)
Saga's major departure from canon is that he's not dead / soul-frozen into a statue to be tormented for all eternity; instead, he’s alive again and arriving on the island. However, due to the combined effects of purging half his self, dying, being undead, and then almost obliterating himself bringing down the Crying Wall he has very limited access to his skills.
As of his arrival on the island, Saga retains his physical augmentations (strength, speed, stamina, durability) but “supernatural” expressions of his cosmo are limited to mindspeech, a basic energy-projectile attack form (stripped-down Galaxian Explosion) and a limited form of mental 'nudging' or influence (stripped-down Genroumaouken). He will not regain Another Dimension or illusionary abilities while on the island.
The Gemini Cloth is weakened on arrival and, without a suitable smith, Saga will be extremely reluctant to make use of his armour. He will prefer to rely on his own ability rather than risk the Cloth's death.