Are there historical cases of country A printing the currency of country B for the main purpose of economic warfare?
Very obscure historical example:
From 1287 to 1295, the Danish nobleman Stig Andersen Hvide was leading a band of outlaws from the island of Hjelm supported by the king of Norway against the king of Denmark. Stig managed to kidnap expert coin makers and bring them to Hjelm, where they produced counterfeit Danish coins.
This allowed Stig and his supporters to buy up all the supplies they wanted in Danish merchant cities. The heavy inflation and the problems it caused for the Danish economy made it difficult for the Danish king to afford assembling an army against Stig.