Immortal Grapple, which is a very boss card, works like this:

Once range is determined to be at close in the first round of combat (i.e. after manuvers have been performed), a minion can play Immortal Grapple. Once Immortal Grapple has been played, both minions can only use hand strikes for the remainder of combat, so any additional strikes in that combat must be hand strikes, and if combat continues for another round, range is not determined (it stays locked at close) and still only hand strikes can only be used.
Range is only at short range if the superior version is used.

If the combat continues into a second round, there is no manuver phase. You can't play a manuver card. You can't use a gun to manuver. Nothing. No manuvers. Range is automatically at close.

While two vampires are in an Immortal Grapple, only hand strikes may be used. This means you can use any card that says " strike with hand... " such as Undead Strength, or a previously Torn off Signpost, or punch with basic hand damage, and even use Claws of The Dead, as it modifies your hand damage. You can even use a card for additional strikes (like Blur), as long as all the additional strikes are also hand strikes. You can not, on the other hand, use any Dodges, or Strike: Combat Ends, or any other strike that is not a hand strike. Keep in mind that even the default "1 hand damage" punch that all vamps can use is a strike, even if no card is played.

It is perfectly acceptable to play Torn Signpost, manuever as to stay at close range, play Immortal Grapple, then use Undead Strength to strike for 5 damage (assuming superior Potence) that can not be Dodged or avoided by S:CE, then Blur and beat the victim twice more. If they are still alive, you can press, and do it again, an still, they can not Dodge or S:CE, as Immortal Grapple lasts for the entire combat.

This would make Immortal Grapple look to be a very powerful card, but it can be avoided by manuvering to long range, and staying there, using Fortitude to prevent all the damage (Skin of Steel does wonders against even the best planned Immortal Grapple based attack), or also using Potence to beat any fool who Grapples you senseless. Then there is Thoughts Betrayed, which will prevent all of this foolishness.

Immortal Grapple is best for preventing S:CE, Dodges, and guns. As a gun is not a hand strike, it can not be used in an Immortal Grapple. Not even in an additional strike or on the second round of combat. No guns. No Dodges either. They are also not hand strikes. They are Strike: Dodges. Not even a S:CE. Just a hand strike.
Immortal Grapple is also very useful against Tremere- no need to worry about Cauldrons of Blood, Bursts of Sunlight, or other unhappiness.

There is a question as to what would happen if minion A uses a gun to manuever to long range and then minion B manuevers to close range and Immortal Grapples minion A. Because minion A used the gun to manuever, they must use the gun to strike, but because Immortal Grapple has been played, only hand strikes can be used. Presumably, the minion who used the gun to manuever would get no strike at all in this situation, as they are commited to using the gun (as they used its manuever), but can only use hand strikes, due to Immortal Grapple. Thus, they lose.

Hope this explains everything.
-Peter D Bakija