Countering X

Items
BKB. A well timed Force Staff/Hurricane Pike. Aeon Disk is a special mention because of the despell during the combo, you'll still get dragged back, but his combo will fail. Linken will stop it from even marking you to begin with.

Abilities - any abilities granting invulnerability
Disruption/Astral
Sleight of Fist, Omnislash, Phase Shift etc

Magic Immunity
Repel
Lifebreak cast during X's return will prevent you from returning
Rage

 

duble_dragon already mentioned most methods I can think of that stop it before you get returned.

Then there are also abilities that save allies after they return the targeted hero such as Weaver's aghanims, or test of faith (chen sendback).

 

The best hero to counter the x marking himself is seeker, one well timed rupture and he will take lots of damage going back.
Any other "banish like" skills or items can also do it if team is bad, xmark on allies last 8 second so he can always wait banish to end and bring team member back (because good kunnkas dont xmark themself to xmark push, that is risky).
If you are out of those follow the ilusion pushing counter: You smoke and go from behind to fish the syren/kunnka trying to take the base from 2 screens away.

 

In this regard, your options a little bit more limited. Banish abilities will indeed hold him in place and prevent the X from returning him. If you have vision of the original X mark, glimpse will bring him back (Thunder strike will help with the vision). A well timed meat hook can also fish him out, though this is significantly harder since he controls the return within the 8 second window. Rubick with a stolen X is probably the biggest cheese to keep him where you want him.

 

So far I know, Eul isn't a 100% impediment or counter, because the mark isn't desmontable as long Kunka doesn't returns the spot, but noobs think that Eul or Astral.I, etc... is a counter when in fact Kunka could return the spot after Eul, A.I, etc... ends, depending on which person is playing Kunka, if it's a person with an advanced intuition as well capability to study tendencies such like YajirobeFromDC, Kunka would have most times the last word about it.

The only thing which stops Kunka's mark "cast" is Linken, but for example, if Linken
is on cooldown and Kunka marks the target, then Kunka returns the spot while Linken isn't anymore on cooldown, not even Linken stops it.

Don't listen those trolls on the top.

 

Banish + Global silence! Or you can try to use Distruptor's glimpse. IIRC you can also remove it by casting repel on your opponents.