Riffle shuffle a string - Robbers
Python 3, HyperNeutrino

from random import*
def r(i):
    s=len(i)//2;L,R=i[:s][::-1],i[s:][::-1];o=[]
    while L and R:s=randint(1,len(L));o+=L[:s];L,R=R,L[s:]
    return o+L+R

Try it online!
Proof of Same Character Set