Mongolia dwarfs South America: about 1,560,428 km² km² against 17,840,000 km² km². At true size Mongolia is about 11.4× larger — the whole of South America fits into Mongolia roughly 11 times.
The old Mercator map treated both about equally (2.2× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Mongolia fits 11× into South America.