This creature is just asking to be captured and hidden in a tavern for all-you-can-eat "calamari" night.  Plus it handles garbage disposal and body disposal for those seedier taverns.

Quote from Fajerbol >>

If a 5-level fighter takes their turn before the roper and action surges to roll 4 attacks and one bonus attack from something like GWM against the Roper, the creature attacks only two times instead of five. He can repeat attacks in the next turn to rid him of all tendrils, then use one attack on each subsequent turn to counter the re-growing tendril and the other to attack the creature itself.

It renders the Roper's ability to control the battle nearly non-existent and leaves them only with its bite. If noone attacks the tendrils, he should keep characters away or restrained forcing them to waste actions and attacks on its tentacles.

GWM doesn't grant a bonus action attack unless you crit or kill something, which you won't be. And the ropes have 20 ac and 10 hit points, meaning you're not likely to break a tendril with every attack. You just burned action surge to deal 0 damage to the roper. 
Okay, let's say it only has 2 tendrils left, fine. It only needs to restrain the nearest character to get a bite attack with advantage in. 
Or the roper is on the ceiling so you can't hit the tendtrils until it has attacked with them. 
AND how are you going to beat it in initiative, if it uses false appearance to ambush the party with a practically guaranteed surprise round?

Quote from NathS >>

The wording on Grasping Tendrils is ambiguous enough that I'm unsure if it's only able to regrow one tendril per turn, or if it can replace every broken one at once.
On one hand, it says it can "extrude A replacement tendril" at the start of its turn, which sounds like it can only regrow one...
but on the other hand, the way it's worded, that's attached to a tendril being destroyed, and could apply separately for each destroyed tendril.
I think, personally, it might be a little weak if it can only get one back per turn, but getting them all back at once is too much, and would feel bad if the PC's are trying to destroy the tendrils as a strategy. I would suggest perhaps rolling 1d4-1, or something?

Remember it has 6 tendrils in total for 4 tendril attacks, which would be pointless if they could regrow all their tendrils at once. 
The tendrils are also hard to hit (especially if you are restrained) and don't have stats and are not creatures, meaning that Rules-As-Written, they aren't affected by most AoE spell (not how I would rule it but still). 
It only needs one tendril to pull the nearest person in for a big bite, and if the party put in the effort to wreck all its tendrils, they earned getting to fight it in a weakened state. 
They'll have to keep breaking the tendrils or flee if they fail to kill it quickly too, or it'll get back up to fighting shape in no time.

Quote from DruTheBear >>

So what good would attacking a tendril do, if the Roper can just replace it for free? Does it take an action to replace the tendril? Or would attacking the tendril be purely for releasing whoever is grappled?

🤷

Quote from The_Random_Bard >>

I'm gonna have to nerf this. 20 Natural AC? Insane!

Quote from HeWholsMe >>

I think I would nerf its health, and as that its fleshy interior is just really weak

 me using him right now wish me luck

got thrown at one of these at level 1, what the hell is wrong with this dm :sob:

Lvl5