Nice sheet

Sea Snakes mate, Sea Snakes 

If the snake has an attack of opportunity and uses bite- and the bite hits the target, is the target grappled?

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. To make the opportunity attack, you use your reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves your reach.   You have to use the constrict action not bite action but yes it is a melee attack so it would auto-grapple on hit and drop their speed to 0, preventing their escape.  

i think i figured it out (maybe), i think its a 15x15 when coiled, so when spread out its 45 ft long (if its 5 ft wide) 

I’m waiting for the Titanboa, or I can just home brew it I guess

Each square is about 5 feet squared, so it would be at least 11 by 11, as it cannot fit in a large (10 by 10) area

I love these things 

I know I am very late, but anyway, the real catch is that the grappled status automatically breaks if the target it tries to grapple is too big, to be exact, if its 2 sizes larger, oh wait, this thing is huge, there is only one bigger size, terrasque sized/ancient dragon sized, so yes, this thing can grapple anything, it is just that big of a snake.

I found this: DND monsters plus some that you have to buy. I linked the website and your desired Titanoboa stat block. This is not Homebrew. Anyone can use the links below from this comment, but it is mainly to answer Lasersharks comment

Titanoboa 

DND Bestiary

Anaconda 

The swim speed I believe is primarily meant for traveling across bodies of water, and not for actually diving underwater. 

love it

I agree a hyperlink would be nice, but it's been 5 years.

Quote from EnchantedNinja12345 >>

Shouldn't this have a higher AC?  It's thick and scaly.  This has less AC than a wolf, even though it's bulkier and has scales instead of flesh and fur.  

 Being huge, it gets -2 to AC. Partly explains the low AC

true

I was imagining something like this. Then that chart was posted. I followed the link in it and it says “The Size Categories table shows how much space a creature of a particular size controls in combat.”. It’s not how big it is, it is how much space it controls. So it can land a strike or attack within  a 15 foot cube.

I named my snake Albert :3

I'm saying it's likely 3-5 feet wide a 40 ft long weighing a couple thousand lbs

Oh my god oh my god read closely I don't have much time the cure to cancer is..........Hello this review has been overridden by the CIA we are sorry for the inconvenience