Hey,
I'm working on an assassin charakter and need some ideas on how to integrate her in a group, as assassins work usally on their own rather than in groups.

Also I'm curious on your ideas for interests or hates of my charakter^^

Maybe the group is working against one of your targets that maybe is hard to get to by yourself.  Or you need to blend in with a group after killing someone to draw attention away from yourself. 

Assassins are really good at killing people, BUT... that subclass also makes you an expert at disguises and false identities and such. So, maybe your character is on the run, hiding out from some Big Bad Guy by living under an assumed identity. Killing is just something you do to pay the bills, but your real focus is on maintaining your false identity and in creating a new false identity whenever you think the Big Bad Guy might be closing in on you. 

In terms of how that would work within the group, well.... your group will inevitably have to negotiate with other people or whatever. Maybe the party needs to book passage on a ship. You could use your disguise kit and the Infiltration ability to assume the identity of a sailor or a semi-famous pirate to try to commandeer a ship. Or the party may need to get a meeting with a city Mayor, so you could use your skills to assume a false identity of some bureaucratic official that needs to get in to see the Mayor for official business of some sort. 

Remember that combat is just one piece of the pie. If you develop your non-combat capabilities, you may not have to fight to the death as often.

Quote from AnzioFaro >>

Assassins are really good at killing people, BUT... that subclass also makes you an expert at disguises and false identities and such. So, maybe your character is on the run, hiding out from some Big Bad Guy by living under an assumed identity. Killing is just something you do to pay the bills, but your real focus is on maintaining your false identity and in creating a new false identity whenever you think the Big Bad Guy might be closing in on you. 

In terms of how that would work within the group, well.... your group will inevitably have to negotiate with other people or whatever. Maybe the party needs to book passage on a ship. You could use your disguise kit and the Infiltration ability to assume the identity of a sailor or a semi-famous pirate to try to commandeer a ship. Or the party may need to get a meeting with a city Mayor, so you could use your skills to assume a false identity of some bureaucratic official that needs to get in to see the Mayor for official business of some sort. 

Remember that combat is just one piece of the pie. If you develop your non-combat capabilities, you may not have to fight to the death as often.

Yeah, focusing on the disguises aspect sounds interesting. It also explains why her team needs her.

How about going for Bard College of Whispers rather than rogue assassin and specialise in psychic assassinations. You'll be able to use your bardic inspiration dice to deal between 2d6 and 8d6 psychic damage when you hit with a weapon attack, combine it with the shadow blade spell. You can still use the criminal or charlatan backgrounds to give that rogue feel but give you a lot more options to being party friendly.

Do you mean ASsassin in concept? Or Assassin the rogue subclass? (or both).

i like the retired assassin who left to try "a normal life" but gets roped into things whle trying to hide their skills, but getting comfy over time.  There is a good manga like that; forget its name though. but the guy quits and becomes a guild employee(nobody), and just enjoys a fairly normal life training folks.  When  asked why he's skilled it chalks it up to having to know a lot to be a good guild representitive.

If you're just looking at the concept. then I'd honestly look at mixing and matching some Warlock and Rogue Assassin together.  Warlock gets a lot of tasty invocations for setting things up; as well as the ability with blade pact to have your weapon on you at all times and easily hideable.   Mask of many faces and the like can help as well.  

I thought of a changeling rouge with the phantom subclass to make it more interesting, maybe one of the victims gave the charakter the connection to the dead, maybe not even on purpose

Perhaps your character was an assassin who was in it for the money. One day, whilst on a job, they saw a party of adventurers arriving back from a quest, with people celebrating them in the streets, and they decided then that they wanted not just the riches but also the glory. They left the profession to go adventuring, either being open with the origins of their skills or trying to pass them off as skills learnt through their childhood on the streets, but you make enemies when you're an assassin, and you can never really leave - giving the DM a lot of meat for story arcs and plothooks.

The easiest way of integrating a character in a party is creating a shared history with one or more of the other characters. Once you establish why you might be hanging out with those people, the specifics of when and how you teamed up are easy to fill in. Childhood friend, fellow student under the same mentor, related by blood, sold into slavery to the same master, take your pick. You could just as easily describe a classic "met in a tavern and were hired by a mysterious stranger" scenario as well, and have that happen a couple of months prior to when the campaign starts. The party doesn't have to be a handful of random strangers who only meet on the day the campaign starts.

Disguise is indeed one of the most important qualities for assassins.