Come now, I'd like to keep the historical discussion going on, so let's stick with that.
Check and mate? Excommunications backfired as often than not. Turns out that if the reigning monarch was capable enough, personal loyalty to him outweighted excommunion schommunion stuff, go figures. Quite a few times the pope ended up in dire straits due to these backfires.
And then there's that legendary popefight schism where they ended up excommunicating each other.
Double KO?
That happened all the time back in the day, really. Culminating in the period between 1409 and 1417, when you had
three different Popes, one based in Rome, a second in Avignon, and a third in Pisa. It took the Council of Constance to resolve that mess, by getting rid of all three and putting a fourth one in - well, the Agivnon Pope didn't like it, so there were still two for a while. The Holy Roman Emperor, Sigismund of Luxemburg (a supporter of the Roman claimant - a rare thing for Holy Roman Emperors, but then again the Avignon Pope was supported by the HRE's perpetual rival France), had his own part in the proceedings, also taking time out to burn Jan Hus at the stake. Of course, this (both thises, both the schism and Hus) would ultimately contribute to the appearance of the Protestant reformation in the Empire a century later.
Hm, there's an interesting line of conversation here. Support of the northern princes for the Protestant Reformation: primarily used as a way of weakening the Empire and opposing the attempt of Charles V to resore the Emperor's power?