Shandians and Blood soaked giant (Red Line) are connected with strong proof, what you may have already heard is Giant Snake in Harley is the Giant Snake from Noland flashback or someone who had eaten DF Jormungandr but I found something more which confirms the ome option from these two and may even bring us closer to decode end game... 

The pants wore by Shandians is similar to Giant Snake which they called God in terms of design, the Giant was not plain looking snake it had some design pattern now if we look closely at Harley and the Pant shown you will see the X resemblance on the Giant Snake too because it may not be possible to design same pattern which Giant Snake had so they used X both on thier Clothing and in Harley.

Shandians did sacrifice in the name of Sun God from what I know through the Giant Snake, the Giant Snake in Harley is not enemy of Sun God it maybe opposite and it is also possible Marijois is above Red line to make sure that Giant Snake is not revived again or something like that, end goal will be to set free the Giant Snake destruction of Red Line, they will meet again Sun God and the Giant Snake.

Skypiea is the most important arc but nobody is questioning why WG or Celestial Dragon ever tried rulling Sky Islands, these people have close to no contact with blue sea. Skypieans are also believer of Sun God, if we watch the episode when Eneru was defeated we can see Connis everyone praying to thier God which is Sun God the moment Skypiea was about to get destroyed and Luffy answers thier Prayer by saving them because he is the Sun God. 

Enel goal was to destroy Skyislands and send everyone back below to blue sea because the Gold was found after he came to Skypiea which led him to fulfill another goal of Arc Maxim, he had already erased Skyislands in past. A villain never has a goal without a reason, Skyislands were not there originally as part of the planet it was man-made probably by the Advanced Ancient Civilization or was Creation of Sun God to keep his clan safe because we can all question why the most important arc which has this much end game lore was never touched by Imu and his goons... If in Sky they have Sungod Protection which bars Imu and Celestial Dragons and keeps Sun God devotees safe then Shandora getting pushed to Skyisland was no accident because Noland would have brought the King and thier man on Shandora and not to forget this King was in touch with Mariejois, Mariejois would've killed Shandorians as they were already bieng targeted in Void century that's why maybe Calgara said we are the remaining survivors, the others were killed protecting the bell and poneglyph on the bell. The Ringing of the bell was Holy for Shandorians they called it Fire of Shandora. After only Skypiea we see Luffy getting new moves like Gears starting from Enies Lobby the Ringing of the bell may have been some kind of trigger which started something, like start of the end of Third World. 

As I've talked alot but interesting things I am spilling,  I would like to add one more thing as we know Galley Ra is Frozen in Punk Hazard, but if you remember we entered Punk Hazard fighting a Mechanical Dragon surprisingly it resembles Loki Dragon form and not only that Ryuma had slain a Dragon... Zoro beheaded the mechanical copy of Nidhogg in Punk Hazar so it will be safe to assume Ryuma the Blade God killed Elbaph the God of War. Ryuma and Sun God were partners like Luffy and Zoro. The freezing of Galley Ra was work of Ratatoskr and is the only one who can unfreeze it same as how Boa Hancock powers work, now Ratatoskr died at some point but his mission given by his Master had to be fullfilled so the determination/will of Ratatoskr got merged with Ragnir or simply the will moved to nearest normal fruit and it took Ratatoskr will to fulfill a promise shape of DF and was fed to Ragnir the Hammer of God Elbaph. 

That's it from my end, open for a discussion in comments ✌🏻

Got some good sauce...