In Spain it is legal as long as it can be easily distinguished from real cash and you don't try to replicate security measueres like the metal band, the foil band, the transparency, serial number, etc. We even have a version of monopoly with euro banknotes that are a exact copy of the true ones but a bit smaller (the 5€ banknote from monopoly is the same size as the real old one) but they lack the number on the top left corner, serial number and they are also print in normal paper.
This is even the old 10 banknote, the new one is that:
and includes new anti counterfeit measures (it is also smaller than the old one)