Sorry, but only 2.5 as I am quite disappointed that I was not able to find anything closely looking as fourth costume which brought all my efforts to vain and you, in turn, never responded to any comments of people that had the same problems.
Sad, as I enjoyed the game before the endgame.
*UPD*: Alright, changing it to 3 as I my guess on how to get last costume was correct and I was at least able to get everything in the game - but I had to restart it.
Answer is to choose John in a pumpkin drama mini-quest (i.e. do not speak to lady-pumpkin after speaking to Mark aka "friend" but speak with the guy behind the doors).
Still finding the costume and finding everything was not satisfying as it had absolutely no impact whatsoever.