Maggin, Novick and Blaisdell handle the story in The Joker 8 (Jul/Aug 76), which pits the villain against the Scarecrow. The Scarecrow had last appeared in a cameo in the Creeper story in 1st Issue Special the previous year.
The Joker is just begging for trouble in this story. He gets the idea to disguise himself as the Scarecrow while committing robberies, after testing the idea out on his own crew. It works on them the same way it works when he pulls off his crime. People are so used to reacting with feat to the Scarecrow he has no need of using any actual fear gas.
When the Scarecrow finds out the Joker has been impersonating him he is not happy at all. He finds one of the Joker's men, just after the guy gets released from prison, and uses his fear gas to force the man to reveal the location of the Joker's hideout. Poor guy, the Joker has also poisoned his system, with one that only works if he reveals the information the Scarecrow forced out of him.
The Joker has been expecting retribution from the Scarecrow, and leaves him a note indicating that he is heading to the zoo. The Joker's men think they are there to steal the hyena, but the Joker actually wants the painting on the top of the cage.
The Scarecrow shows up, and the pair fight it out for a few pages. The Joker switches the canister of fear gas that the Scarecrow brought for laughing gas, which makes for a great climactic scene. The Scarecrow thinks he has defeated the Joker, but in fact has been overcome with laughing gas himself. The final panels of the tale show the Joker sneaking back into Arkham, presumably by the underground entrance to his cell shown in the previous issue.
The Scarecrow returns the following year in Justice League of America, as part of the Injustice Gang.