Wroth of the Dragonlords
This information has thus far been released in a sample chapter for The Winds of Winter, and might therefore not be in finalized form. Keep in mind that the content as described below is still subject to change.
Wroth of the Dragonlords is a mummer's play written by Phario Forel. It is the first play Forel ever wrote. The play presumably deals with the history of the Second Spice War between the Valyrian Freehold and the Rhoynar, in which the dragonlords crushed Garin the Great's army with their dragons. In the play, Prince Garin gives a speech on the eve of battle.
The Winds of Winter
Izembaro, the King of the Mummers, quotes Prince Garin from Wroth of the Dragonlords the night he and his group of mummers at the Gate are set to perform The Bloody Hand, also written by Phario Forel.
It shall go ill for any man who fails me.