Had similar one to my younger brother's & father's stellar obsession with clowns & then things that terrified me coupled with a lot of other obsessed violent psychos -
Is there anything where clowns and mascots would be safe, in a safe setting?
I started small. Thinking of clowns until I could think of the thoughts of looking at one.
Looking at one on the image I could perfectly well rip to pieces any time I wished.
When done looking at images, looking at moving images, from multiple angles.
Changing the time of the day & circumstances I was viewing those, until I stopped associating clowns=danger with all the variations of other factors that triggered me to the original traumata.
Then, safe with the images, even if they move and surprise me and startle me and make me attack 'em, approaching a clown toy. It's a stuffed thing, it can't hurt me. It's a stuffed thing, I can soo retaliate. Months of hilarious exposure & treating clowns as a mortal enemy.
Ok, got this one. Now going to the mannequins in public spaces. They just stand there. They're not moving. Suck it, McDonalds, you're not getting to me, I'm getting my burger and skyjetting out of there. Good me, I got this, I'm awesome hunter, who got the goddamn burger in peace. Shakiness for half of the day followed. :D Doing it again, until manequins are safe.
Then approaching costumed people. Then and only then, and for very short meets. Helloo. You actually look kinda cute in that costume. Nah, you don't, you look trash, but I'm not telling you, I'm looking for the cute parts. Okay. Hey, this hair dye is actually pretty interesting, where did you get this.
Followed by generalizing that. People, even if clowns, are not by default unsafe. True, they're also not safe... but it's not the same phobia. Just people being people.
So start small, baby bits, before baby steps.