How does a GM handle effectively a player that overreacts to any negative effects the player's character suffers, like level drain or death?
[RPG] How does a GM deal effectively with a player unable to lose gracefully
gm-techniquesproblem-playerssystem-agnostic
Related Solutions
Negative Levels don't actually reduce your character level
They basically give you a -1 penalty on a bunch of things for each negative level you have.
For each negative level a creature has, it takes a cumulative –1 penalty on all ability checks, attack rolls, combat maneuver checks, Combat Maneuver Defense, saving throws, and skill checks. In addition, the creature reduces its current and total hit points by 5 for each negative level it possesses. The creature is also treated as one level lower for the purpose of level-dependent variables (such as spellcasting) for each negative level possessed. Spellcasters do not lose any prepared spells or slots as a result of negative levels. If a creature's negative levels equal or exceed its total Hit Dice, it dies.
So you don't actually have to recalculate the whole character, you just have to know what things are affected by level drain, and subtract accordingly. You don't lose any spells, or access to feats, or any skill ranks, etc.
So, really all you need to do is apply a penalty of (negative levels X -1) to all attack rolls, saving throws, and skill checks, and reduce hit points! Spell durations also go down and some other things, but that's not too hard to recalculate on the fly.
This is in contrast to older editions of the game when level drain did actually reduce your character level, so Paizo has baked in to the system a less-crunchy way to deal with the classic level drain problem.
Edit:
It has been noted that in previous editions temporary negative levels could become actual character level loss. This has also been removed in Pathfinder (this section is right after the previous quote).
Some abilities and spells (such as raise dead) bestow permanent level drain on a creature. These are treated just like temporary negative levels, but they do not allow a new save each day to remove them. Level drain can be removed through spells like restoration. Permanent negative levels remain after a dead creature is restored to life.
The scenario will need some adaptation. Your player is now trained to think about these hard-to-hurt monsters as too powerful for him and his characters to deal with.
It's actually a good sign that he runs away when he feels outmatched (see How can I make my PCs flee? for the flip side of your problem).
One system-specific possibility is that he has missed some option which is assumed by the designers. An extreme example is a party of melee only characters against ranged monsters with flight. Take a look at this and see if there are easily available options to deal with the common monster defenses. Make this an extra sidequest so it's not just a GM handout.
In general, there are two feelings a player needs to get involved in a conflict. The first is confidence that he can find a way to defeat the enemy without losing horribly. The second is investment in winning.
There is a balance between these two elements. The more investment a character has (the monster is threatening an NPC he really likes for instance) in winning, the lower the confidence he needs in winning to try. This also applies in reverse. The more confident he is in winning easily, the less investment he needs to get involved.
Confidence is increased when you achieve something a little harder than you expect to be able to do. The classic psychological text on this is Flow by Mihaly Csikszentmihalyi. If you want to train someone up to feel capable of handling monsters that put out these signals, start with much much weaker ones and show farmers/townspeople/NPC nobody's dealing with them. Then build up the opposition until they know how to handle the ones you care about or have worked out the tools they need.
In the specific example of the Eerie, you need to signal that all is not quite right with it. Give someone a skill check, Knowledge, Nature Lore, Perception, whatever, to see that it's not exactly what it seems. That should give a little boost.
Building investment is a big task. Creating emotions and How can I increase tension during roleplaying? have more advice to give on this subject.
Best Answer
Stefano, I am a GM and one of "those" players. The main thing that makes me hesitant and generally concerned about my character gets killed comes from a few sources:
Your player probably has different reasons. But, for me, the "fix" is not to play a care bear game or to ruthlessly me off until I leave or "get over it." the fix is, play a system where the stakes are known. I am perfectly willing to risk character death for the "right" reason. Everyone talks about how cool it is when their character dies for glory. I wouldn't know, I have only died because the GM rolled a double crit...
For instance, Shadow of Yesterday has a "free and clear" phase where you can negotiate what you get and what you risk in a roll. While Dogs in the Vineyard has Stakes setting and a "Give" rule where you can just concede the Stakes without risking character death. Finally FATE has Consequences and Concession. These are all games where the Player has more control over when their character lives and dies. But it does mitigate or prevent risk. Most of these players are not risk averse, they just want a means of risk assessment.
So, that would be my advice, try one of these games and if that doesn't work out, then you need to figure out what is really going on (it probably doesn't have anything to do with their character death then)...