When Boss's Chauffeur dies, its second ability and Together Forever trigger.
Resolve the Boss's Chauffeur trigger, creating at least five 1/1 Citizen creature tokens.
Resolve the Together Forever trigger, returning Boss's Chauffeur to your hand from your graveyard.
Activate Phyrexian Altar five times by sacrificing five Citizens, adding ({5} magic symbol) .
Repeat.
If you control five or more creatures to start the combo, this combo will net infinite Citizen tokens, infinite +1/+1 counters on Boss's Chauffeur and infinite colored mana.