Predictions for new support
First I'll give my analysis of the post.
Never Turn Your Back On The Sea
Let’s reset a bit and wade right into the next champion we’re adding to the list. We felt it was time to execute on a new support with a darker, deeper thematic than most of our support cast. We also wanted to create an aggressive playmaker, someone who doesn’t just save a drowning ally, but who forces their enemies to drown themselves… by their own hands. Keep your health high, your eyes to the sea, and pray you aren’t on the list.
** Title: "Never turn your back on the sea"** makes me think that they'll be more powerful vs enemies that are trying to run away.
"Let's reset a bit" to me suggests this champion has reset mechanic like Irelia's Q.
"time to execute" makes me think this support will have an execute mechanic.
"darker, deeper" probably deep sea themed.
"aggressive play maker" suggests they fit into the class of vanguard, catcher, controller or assassin as their playstyle.
"save a drowning ally" maybe something like thresh's W.
"forces enemies to drown themselves" could mean some sort of punishment mechanic where enemies are CC'd or damaged for performing some action such as moving too far away from this champion or using abilities etc.
"Keep your health high" further indicative of an execute mechanic, or at least that this champion becomes more effective when there are low health enemy champs nearby.
"your eyes to the sea" suggests you have to be watchful. To me this brings to mind stealth as a mechanic that would warrant you having to keep an eye out to make sure this champion isn't coming for you.
"pray you aren't on the list" pray could be indicative of this champion being some sort of deity! or at least related to one. On the list could just be purely a lore thing or it could mean a bounty board system like Rengar or a hunt system like Kindred.
Now the picture.
So what we have here is a view out of what appears to be the window of a sunken ship. This could mean that this champion could be some sort of undead pirate that sunk with his ship.
Outside the window we see a lot of what look to be sharks which make me think that this champion is related to sharks. Either using them possibly as a pet that enter a feeding frenzy vs wounded enemies (execute mechanic), or they themselves being some sort of shark creature that is stronger vs wounded enemies.
Beyond the sharks is a large creature that I guess could be a whale or some sort of sea monster like a leviathan that this champion might summon.
My best guess from what I've gathered from this post is that this champion is some sort of shark-like aggressive assassin/support hybrid that may have a kindred-like passive that incentivizes a roaming playstyle. Being a water based champion, perhaps they gain something like bonus movement speed and perhaps stealth while in the river. I'm fairly certain this support will be uniquely strong against low health champions and bring the a punitive effect to the game as well as some sort of bail out move for allies along the lines of a thresh W or perhaps a CC cleanse since they're able to save an ally from drowning (in CC?).