Yeah in that phase people have to defeat all the previous bosses in a row first. If at least one boss won, Hydra won't appear. Murk -> Ares -> Athena -> Kalibak and Steppenwolf -> Hydra. If Hydra is to spawn, there will be "Hydra stirs, prepares to awaken" message. If not, it will say "Hydra continues to slumber, unawakened" instead and the cycle will start anew.
After Athena it's Kalibak & Steppenwolf and they must be defeated, then Orion (Must be defeated as well) and it takes a couple minutes for Hydra to spawn after. It usually says "Hydra Stirs, preparing to awaken" something like that.
If people defeated bosses before you joined them, it doesn't matter when you join. It's not group-based, it's phase-based. Plus, bosses spawn at fixed time with whole cycle taking 30 minutes. They spawn at the same time in every phase, which makes it like this: Murk: xx:00, xx:30. Ares: xx:05, xx:35. Athena: xx:10, xx:40. Kalibak and Steppenwolf: xx:15, xx:45. Hydra (if all are defeated): xx:20, xx:50.
You only fight Orion if you defeated Kalibak and Steppenwolf quick enough. Otherwise he simply joins the fight against them.
Just to clarify - Orion does not have to be defeated for Hydra to spawn. Orion will join you if the fight is going too long with Kalibak and Steppenwolf or he will attack you if you snatched victory from him before he got there. Orion has feats associated with him and a rare drop (Mother Box combat pet - different from the Father Box you see in Solo and Raid). Edit - you guys type fast. Oops.
im still trying to wrap my head around why he is attacking us for the reason of beating them? we beat 2 people before he got there to help us.... wouldnt a congratulations be in order, not a "alright fight me!!" this would be like the justice league getting fighting us because we beat their main adversary before they came to help.
I think the idea is that Orion is a hit first, ask questions later, sort of hothead. I mean, it's hardly as if there's no precedent for the first time when heroes meet, they fight before realizing they're on the same side. That's practically a trope required by law in comics, I believe.
Maybe listening to (or reading subtitles) what Orion has to say when he spawns might help. If he appears hostile he has the following line: "My fists will not be denied! It matters not who I must take the Source fragments from!" If he spawns when you're still fighting Kalibak and Steppenwolf, the next dialogue between Darkseid and Orion occurs: "So, my son. You nip at my heels, even here? I will not forget this slight." "Father, do you think New Genesis would allow you all the Source Power? No! Highfather sent me to challenge your might! Kalibak and Steppenwolf! Stealing for Darkseid? I will destroy you and take those Source fragments back to New Genesis myself!" He really is that kind of hothead that wants to beat up somebody.
