How I would think the TF2 mercenaries would interact with THT Freddy
Scout + Freddy= Scout teasing Freddy on not being able to double jump
Soldier + Freddy= Soldier yelling at Freddy that he (Freddy) isn't American
Pyro + Freddy= Pyro cuddling with Freddy's gut because Pyro is a psychotic but adorable thing
Demoman + Freddy= Demo sharing his beer with Freddy
Heavy + Freddy= Heavy and Freddy eating sandviches together.
Engineer + Freddy= Engie showing his creations to Freddy.
Medic + Freddy= Medic operating on Freddy to see how he works on the inside.
Sniper + Freddy= Sniper probably having nothing to say.
Spy + Freddy= Spy disrespecting Freddy for how fat he is, eventually building up to Freddy voring Spy.