When I have managed to get my credentials by ssh-agent I still don't know which ssh client command I am supposed to use then. mysysgit and putty's plink don't seem to profit from the agent.

I managed to "install" the native library by adding the path to the dll to the path and then restart Jenkins.

Then it always crashed if my credentials were not in putty's ppk format. Still I cannot execute a plink command. I'm not really sure why. I'd assumed because ppk was the only valid format for me, that I would have to use putty's commands.

Before I had tried mysysgit's ssh command which doesn't seem to have the correct passphrase either.

This job is successful, but the command is not really executed, as if the passphrase is still necessary and just not entered. If I enter the same command in cmd and enter the passphrase the command is actually executed.

Here's my output:
Started by user Admin
Building in workspace D:\jenkins\workspace\freestyletest
[ssh-agent] Looking for ssh-agent implementation...
[ssh-agent] Java/tomcat-native ssh-agent
[ssh-agent] Skipped registering BouncyCastle, not running on a remote agent
[ssh-agent] Started.
[ssh-agent] Using credentials test-ppk
[freestyletest] $ cmd /c call C:\Users\tcbld1\AppData\Local\Temp\2\hudson7374457953271842666.bat
CLINK D:\jenkins\workspace\freestyletest>E:\putty\plink.exe -i C:\Users\tcbld1\.ssh\converted_for_putty_jenkins_id_rsa.ppk target-machine -l testuser touch plink
Passphrase for key "imported-openssh-key":
CLINK D:\jenkins\workspace\freestyletest>exit 0
[ssh-agent] Stopped.
Finished: SUCCESS