Uhm, it actually already should remove any x-speed from actors when near center and smash them hard into the pit!

Hmm...
I tend to have the victims continue jetpacking, meaning that they fly above the pit and off to the other side - allowing them to recharge the jetpack before the process is repeated a few times.
Also, I often play long enough to wear down the bottom of the pit, so that doesn't help either.

Well, do you have any suggestions? Shall I have the bottom of the pit regenerate over time with some pixelspam(tm) magic?

You could probably just make the bottom of the pit the darker, more packed together dirt more commonly found near the bottom of the screen, but it doesn't actually matter that much - games that last long enough to wear down the bottom and sides of the pit are not commonly played by many. You'd really be solving an extremely minor problem that barely affects anyone.

Perhaps it secretes some kind of organic 'concrete' in a wide spread (90 degrees left right and down), and by the time the hole's patched up, the emitter is blocked by concrete, and can't emit anymore particles until the hole is made again. Problem solved.

Add an extremely infrequent mopixel drawing script. If you need one I can explain the basic method and/or post the code Kyred, TLB, and I have worked out. If you want to optimize it somewhat you can also add in GetTerrMatter checks so it'll only replace displaced terrain.

a way to kill it is might to throw like a bomb over it not in it and hope it grabs it or fly over it and fire franticly at a core deep behind a vine wall and hope it can't grab you

Er, what? You're suggesting a way to kill it right? Because it's currently invincible.

I thought about having to place some kind of core, and a vinepit must have atleast one core somewhere around it. When the core dies, the pit does also.

Maybe you could have a core that only has GetsHitByMOs = 1 when it's grabbing something.

Maybe some sort of herbicide bomb would be able to kill it?

It pulls things to the core, which is only vulnerable while chomping them, and insta-kills things, so you would have to throw in a grenade for it to grab.(Not sure if it grabs grenades right now, but it should.)

Not even Whitty's Rape Bomb could kill it...

hmm how bout to kill it you have to light it on fire

for me the actor is flung around(left and right) until they die , this wears away the pit walls very quickly , and ruins the point of the vine pit.