So, when the Dragon perches on the center of The End Island, she does her Dragon's Breath attack, and the Dragon's Breath has a really exploitable feature to it.

Normally, the Dragon's Breath AoE would decrease overtime and then disappear, that's how it works for the fireballs and that's what I thought it worked for the breath attack, but I was wrong with the latter. Once you bottle her breath attack up, there's something you can see: A very small hitbox of Dragon's Breath AoE, minuscule. If you bottle that small hitbox, then the AoE will grow in size with each subsequent bottling, resulting in an insanely huge Dragon's Breath AoE.

Of course, the AoE disappears either when the Dragon does another breath attack or once it's timer runs out, but this seems to be a pretty good exploit for PvP in The End and getting huge amounts of Dragon's Breath in a short span of time.