User blog comment:TheBlackDragon4/Death Battle Continuity?/@comment-5035900-20181114205444

It's pretty difficult a task due to a vast majority of Death Battle's not having continuity with others. The major exception is both Goku VS Superman episodes, with the first acknowledging Vegeta VS Shadow, and the second having both Goku and Superman acknowledge having fought before.

Other than that, returning characters don't really treat returning as anything new (other than Deadpool because he's a fourth wall breaker), and while similar city and desert canyons were used in several episodes, none truly seem to try to actually cross over with other episodes. Then there's cameos, such as Captain America's, which doesn't necessarily guarantee that it occurred before his Death Battle, as it could very well have been a different Captain America from the one that faced Batman.

In spite of what I just said, I'll give a helping hand with the most definite cases I could see:

The TMNT Battle Royale occurred before Zitz VS Leonardo, as Wiz and Boomstick acknowledge the prior battle between Leo and his comrades.

Vegeta VS Shadow happened before Goku VS Superman, which was followed by Goku VS Superman 2.

Chuck Norris VS Segata Sanshiro took place prior to Guts VS Nightmare, Naruto VS Ichigo, and Strange VS Fate due to their constellation appearing in two of them and themselves still fighting in Naruto/Ichigo.

Good luck with the remainder.