His attackers rifled through his pockets as the victim lay helpless on the ground.
Callously, two of the three robbers returned and forced him to hand over his PIN, before £200 in cash was withdrawn from his bank account on May 19.
All three attackers were todaylocked up at Mold Crown Court.
Defendant Thomas Kiely, 19, of no fixed abode but who came from Manchester, was sentenced to a total of five years youth detention – four-and-half years for the robbery and a six-month suspended sentence was activated.
Kiely, who had the knife, admitted possessing the blade, blackmail by forcing the victim to hand over the PIN and theft of the money.
Pregnant mother of five Victoria Emma Cullen, 34, of Coronation Drive, Chirk, said to have initiated it, admitted robbery and common assault and was jailed for three years and four months.
The judge said he appreciated that she was pregnant, which he said was a decision she had made since the proceedings began.
Bradley Jones, 19, of St David's Crescent, Wrexham, who had never been in any trouble before, received a two-year youth detention sentence after he admitted robbery and blackmail.
Judge Niclas Parry told them that it was a serious and depressing case of street robbery which would "sicken right-minded people".
They knew they had found a vulnerable victim in Polish man Mariusz Gaca and they had "gone back again and again" to take advantage of him.
He said they had not only taken his property but repeatedly used violence upon him.
"At no point during this sustained incident did your victim offer a shred of resistance, such was his vulnerability, a man with mental health difficulties alone on the street at night," Judge Parry told them.
Victoria Cullen approached him initially and for no reason repeatedly punched him to the face and body and verbally abused him. The two others then spoke to her, saw their opportunity. They covered their faces and pulled their hoods up and "went for him".
"He was sitting on the floor, such was his confusion after being beaten up," said Judge Parry.
Kiely produced a large knife, Mr Gaca handed over his wallet and they both rifled through his pockets.
His passport and bank card were stolen.
Cullen then "cruelly returned and continued to punch him to the face and head",
They walked away but Kiely and Jones returned as he was sitting on the floor by a cashpoint machine.
Kiely struck him to the back and to the back of the neck repeatedly and he was threatened to hand over his PIN.
Jones stood with the victim while Kiely withdrew the £200.