Back in 2004 relnqshd made a patch which allowed you to fight all the Sinistrals as well as the Egg Dragon simultaneously on Doom Island.
The Fierce Battles
Now it's time to enter the second round of fierce battles. Now the fearsome five await you at the deepest bottom of the Ancient Cave. And for those who don't feel like going down all the way... Like the first version there's also a surprise battle, too. Whereas back then you had to fight what you see at the end of the video, now you also get a similar surprise when fighting a certain wish-granting dragon.
The New Fierce Battle now is part of the patches. The link already is updated.