This seems to me a pretty basic question, but I can't find a definitive answer in the rule book:
Let's say I control a PC that took 3 wounds and a 4th one has put him incapacitated. He also have an injury. What happens when a nasty ghoul shamefully attacks him while he's lying on the ground and he takes a wound again? Does he makes one more roll on the injury table to get a second injury? Does he ever die?
Once an PC is incapacitated, one of two things can happen if they are attacked and wounded again.
The first is that the GM might rule that a finishing move applies, in which case they would automatically die.
If for whatever reason the GM ruled that a finishing move did not apply, then they would have to roll on the incapacitation table again.
Deciding which of the above applies would depend on the individual circumstances, and to a certain extent also the genre and feel of the campaign you were playing in. As commented in this post on the official forum for example, an indirect attack such as a grenade, would likely not count as a finishing move, and there are other posts that suggests ranged attacks generally would not either.
This question could actually be more detailed, as there are various factors that could change how this type of situation is handled. I'm assuming the character has already burned all of his Bennies at this point, and cannot Soak.
First, does the character have any Edges which alter how Incapacitation or Death are handled?
Hard to Kill (Improved rolls on Knockout Blow and Injury Tables) Source: Core Rulebook
Harder to Kill (Chance to cheat death) Source: Core Rulebook
Damned (Return as Harrowed after death) Source: Deadlands: Reloaded Setting Book
Arcane Background (Super Powers) could also apply a variety of effects on these situations (Hardy, Super Edge, Super Attribute on Vigor, Regeneration, etc.). Source: Necessary Evil; Super Powers Companion
Given the enormous number of main line and third party setting for Savage Worlds, I'm guessing there are others out there as well.
The Full Edition & The Explorer's Edition both describe rules for being sent to the Knockout Blow Table more than once (Multiple Knockout Blows, page 68 in the Full Edition; Multiple Incapacitation Results, page 76 in the Explorer's Edition).
The Deluxe Edition does not have an entry for this, but one could inference that the rules would work the same as each damage roll must be considered independently for the purposes of Soaking, Shaken, and other effects.
Savage Worlds Deluxe describes a number of Setting Rules which may or may not apply here. Setting specific rule books will have many more, but this covers a lot of ground.
This is unlikely to help the heroes, assuming they are not cult leaders, but could be applied to prevent Finishing Moves and/or death in similar situations involving villains.
This works essentially as the name implies, adding a cinematic/literary deus ex machina to preserve the heroes against all odds. A version of this applies in the Necessary Evil setting and is present in other Super Powers rule books as well.
The character might use this rule to take advantage of Hard to Kill and/or Harder to Kill in this desperate situation.
In the Deadlands: Reloaded setting, heroes have a chance of returning from the dead. A modified version of this rule could be applied to any homebrew setting.
Finishing Moves do not apply to every situation. The RAW indicate that special situations such as particularly tough or armored victims, chances for escape, and other mitigating factors may apply. In general, this action must also be performed up close and personal (I'm assuming your Ghoul meets this criteria), although some ranged attacks may qualify. A great deal is left to the discretion of the GM.
This is automatic unless the GM decides there’s a special situation, such as a particularly tough or naturally armored victim, a chance for escape, and so on. The killer must usually dispatch his foe up close and personal, but the GM may occasionally let finishing moves be performed at range. Page 64 in the Full Edition, Page 68 in the Explorer's Edition, Page 73 in the Deluxe Edition
Along that line of thinking, different groups will have varying comfort levels and preferences for handling not only character death, but Finishing Moves specifically. In my experience, many players are extremely attached to their characters, and may not appreciate you dispatching them with a single blow when there are written rules for handling additional damage beyond Incapacitation. I have found that it is often a good idea to give the player the option of accepting the Finishing Move and preparing a new character or going back to the Knockout Blow and Injury Tables, potentially debilitating the character or even killing them anyway. As this is solely a matter of preference and opinion, your mileage may vary.
Should you opt not to use a Finishing Move, that doesn't mean that you have to be nice. Against a helpless defender, a melee attacker would certainly be able to apply The Drop and either Wild Attack or a Called Shot (to the Head, obviously) to ensure a Raise and additional damage. Gang Up bonuses may apply as well.
Yeah, the Ghoul should get an advantage, like The Drop (+4 attack and damage) or Finishing move, depending on if the target is simply unaware of the threat or helpless to defend himself.
Upon taking another wound, I would roll them a second injury, then let them roll Vigor if its permanent (hard to kill may apply).
Then I would have them roll Vigor and Spirit again (just rolling spirit in the core rules was too easy to shake for me) if they fail either one, they're incapacitated again.
Then I would have them roll vigor one final time (hard to kill applies here).
On a raise, they would normally be shaken, but since they're already down that would mean no effect. the hit would just be flesh wound. On a success, they would add 1 hour to their knockout time. On a failure, they would start to Bleed out and roll on the injury table again (bleeding causes another injury) and vigor roll to see if its permanent.
When a character takes 3 wounds and starts Bleeding Out, that's usually a sign of certain (and dramatic) death. Even two wounds would get there, if they have no bennies and high penalty on their vigor roll.
On my scenarios I usually take joy in figuring out whether my NPC thugs just get knocked out or slowly bleed to death.
