During the fourth adventure of the ghosts of saltmarsh, the character of one of my players dies right next to a certain altar.

He had bad luck with the dice and it was/is his first character ever. So.. I feel bad of killing him of.

I thought he could awake in front of the goddess (you know - the spidery goddess of the altar), who would offer him to ressurect him, if he would agree to certain dark things.

As the death came to me as a surprise, i did not think about such a deal and I need help to figure out, what the goddess would make him do.

Any ideas?

You could definitely resurrect him with consequences.  Stat penalties for example.  Or he could have to do a quest to repay the goddess.  Or perhaps he is resurrected as a different sort of organism entirely, spider-like perhaps.  

Alternatively, I let me players assume control of a NPC that they already know, who has been in the world for some time.  I usually make the NPC 1-2 levels less than their previous character.  The story goes on, and there is only a minor penalty for dying.  I think this is a win-win alternative.  

Consequences can be fun for the player. I had one who was killed by a swarm of spiders. He got resurrected but had to do a quest in return but also had a fear of spiders and bugs. Had to do a wisdom save or he would panic and run. It was fun and unpredictable for the group

The spider goddess might have goals, laws or ideals that it wants the player to accomplish. If you have seen or read Moon Knight, Moon Knight is brought back to life by Khonshu but he must be in Khonshu’s service. The character might be immediately sent on a quest to serve the spider goddess, or maybe they are left to their own devices but know that the spider goddess might call on him at any time to serve her.

I think the simplest solution is to decide on a specific magic item somewhere in the world that the Goddess wants. Whatever the player does to get it doesn't matter... she just wants the item delivered to her. This way the player doesn't feel that suddenly they're forced to be evil or do an evil thing... like, if she told him, "Kill 100 puppies", the player is more likely to just opt out and create a new character.  The thing she's asking for could prove to be more complex, however... maybe it's something that a remote village is relying on just to survive, or maybe it's a weapon that empowers some truly heinous people.

I also think it would be fun if you were to resurrect them as a reflavored Dhampir from Von Richten's Guide to Ravenloft. The race is designed so that someone could change from another race into a Dhampir, which grants Spider-Climb natively, and a bite attack, which both seem like things you could reasonably gain from having spider-like powers. I'd say check with your player if they're willing to make that change... not everyone wants to completely change race, especially when it's their first ever character, but it would be a quick way to show that their resurrection came at some kind of cost without forcing them to, say... multiclass into Warlock or something like that.

Quote from HSThomas >>

During the fourth adventure of the ghosts of saltmarsh, the character of one of my players dies right next to a certain altar.
He had bad luck with the dice and it was/is his first character ever. So.. I feel bad of killing him of.
I thought he could awake in front of the goddess (you know - the spidery goddess of the altar), who would offer him to ressurect him, if he would agree to certain dark things.
As the death came to me as a surprise, i did not think about such a deal and I need help to figure out, what the goddess would make him do.
Any ideas?

Talk to the player; see if they want their character resurrected.

If the character was some form of religious (Cleric, Paladin, even Druid or maybe Ranger) - whatever goddess they worship, may stop their spirit from ascending and explain that they have still much to do in the world. 

And they send their spirit back to the body.

I had a similar situation; where a player (first time playing) just had some horrible rolls in a battle against some low level demons types.

And failed their death save.

Offered to resurrect them and give a warning from their goddess that they have foreseen a war in heaven.

The player declined, and decided to make a Warlock.

So see what the player wants.

If they want a new character, find a way to bring them into the adventure quickly. Found in a prison cell near the party, or something.