"Basics?" Uhhh... Osiris was super successful at being a Warlock, finding revelation after revelation into all that he did (Ahamkara, Nine, Darkness, Vex, Light, Thanonautics, ect). After the Battle of the Twilight Gap, Osiris was exiled. He left willingly (and probably would have left eventually). The Speaker felt the need to do this because Osiris inspired people to abandon protecting the City in its most immediate form (Kabr went to the Vault because of Osiris and Warlocks shifted their focus from the Traveler). So when Twilight Gap happened, the Speaker felt a need to refocus on the City's needs. While Osiris did hurt the City in this way, he is who is going to save all of humanity in future Destiny games (he seems to be the main quest giver in Destiny 2) He went to Mercury and entered the Vex Gate Network (symbolically or literally losing his body along the way, so that his Light could freely enter. Similar to Toland's current state). Through the Vex, he viewed how time connects- and became somewhat obsessed with patterns. Just like the Vex. He first entered the scene through HoW. He teamed up with the already existing partnership of the Queen and Eris to stop Skolas. Osiris is also the reason Oryx came, and he trained us for Oryx (among other things) with Trials. There is more to it, specifically with what went down on Mercury and how he is bringing in the Nine, but this is getting long.

Why is Osiris the reason oryx came?

Fastest way to answer that is by telling you Osiris is the man in [url=http://www.ishtar-collective.net/cards/ghost-fragment-the-queen-2?highlight=Queen+2]Queen 2[/url] Osiris's introduction: [quote]"Your Grace," said the man before her at the foot of the stairs. His voice was soft but strong. When he spoke the Hunter started to turn her head toward him, then flinched as if someone had shone a bright light into her eyes.[/quote] The trio agrees to end Oryx: [quote]...I will do anything—" her low voice shook with passion— "to end Oryx."... ...Then a small smile curved the Queen's lips. "Well said." She straightened, and leaned slightly forward so the room's light fell on her face. "So let us end him."[/quote] That is the exact "Osiris was involved in Oryx's coming." The specific answer for Oryx is the Queen, Eris, and Osiris baited him. Its more important that it was Osiris because the Queen is off doing mystical stuff and Eris's revenge story is complete. Both now view the Guardians as the key, though both will return later. Osiris is where the story goes next. He also predicted Crota and talked about Oryx before anyone else The "why" of it all is cooler. Though that deals much more in theory than any hard proof pointing.

I agree that Osiris was involved in the plan to stop oryx (I agree him to be the other unnamed person in the meeting between Eris and Mara) I've just never heard and read anything showing Osiris being the reason Oryx came.

Maybe bad phrasing on my part. Crota was [i]the[/i] reason Oryx came. For all intents and purposes, the answer to that is Crota's death. Crota's death happened because of Eris (and Guardians and Toland, but Eris was critical) Eris is a part of a duo with The Queen (they meet in secret a lot) Skolas enters the mix and Osiris joins the Queen to talk about Skolas (I would assume because he almost harnessed Vex prophecy with the Oracles. The Vex being something Osiris is very close to. If not that, it probably had to do with the whole message about the coming darkness). These three group up to stop Oryx. Eris does it to really put a dent in who killed her friends (among other reasons), Queen does it for her wierd motives (her death was a part of the plan), Osiris does it as a step in the pattern to our reclamation (Oryx's death triggers something. Its been a year or so since I really looked into it. It had to do with how the Nine are weak when they touch our world) That trio is the key group in everything Oryx.

I agree with this. They were ones who put in the plan in place and the main reason we were able to stop Oryx. I just got hung up on the words "Osiris was why oryx came".

[quote]"Similar to Toland's current state".[/quote] Wait, what? I though Toland was dead?

Toland is...dead...but only in the terminology that he has died. Because he knew the song of the deathsinger, because he understood death, Toland was accepted by the killing as a friend. Hearing the deathsinger's song killed him, but he turned the song into a conversation. Toland and the Deathsinger chatted and, long story short, Toland is now just his Light flowing in the Hive overworld- mapping the connections between Throne worlds.

Woah, I thought he was just some creepy warlock that died in the moon.

Great answer