Taminos first few lines are:
Zu Hilfe! Zu Hilfe! sonst bin ich verloren, /
der listigen Schlange zum Opfer erkoren –
Here this is translated to
Help me! oh, help me! or I am lost /
condemned as sacrifice to the cunning serpent –
So as PiedPier correctly states, it is definitely serpent or snake, but I see no real problems replacing that by another beast; ...
In the opera Tamino is pursued by an enormous serpent or snake, which is then killed by the attendants of the Queen of the Night. The exact nature of the beast is not relevant to the rest of the story, so it's quite possible that some productions might have given the creature legs and made a dragon out of it. In Schikaneder's libretto and Mozart's original ...