i think the freakiest i could write till (without delving into nsfw (which gives me poison damage to write and also only happens once in a rare moon when i'm possessed by an ancestral spirit or something)) was himedere till seen here

but for freaky tills that match ivan's freak (because i don't know if he can outfreak ivan that's kind of a tall order) i recommend most if not all of ash quillifer's catalogue here. specific fics i would recommend are:

1) at what point do you stop calling it a crisis and start calling it a kink? -- till thinks about ivan's hair and attains something of an oral fixation
2) accidents happen...but maybe not that many times -- pee ft ivan being a freak but till is weirdly into it so i think that counts
3) what's another bad decision or two? -- exes to lovers ivantill where till can't stop thinking about sex with ivan because everyone else is mediocre and deeply vanilla and therefore disappointing

those are my top picks!! but other selections include (not hyperlinked bc it's a hassle to do it everytime):
https://archiveofourown.org/works/57263413
https://archiveofourown.org/works/58389178
https://archiveofourown.org/works/57654796
https://archiveofourown.org/works/59326204
https://archiveofourown.org/works/56984110
https://archiveofourown.org/works/57373288
https://archiveofourown.org/works/56695150
https://archiveofourown.org/works/55701277
https://archiveofourown.org/works/59423026
https://archiveofourown.org/works/60417700

hope that fills you up anon (salutes)