Death Battle/WMG

In-universe reasons as to why some Death Battles were as they were
Doomguy VS Master Chief: Why is Doomguy sluggish and tanking every hit? Why is Master Chief able to deflect all of the chaingun's bullets like that? They aren't the real Doomguy and Master Chief, just two other awesome (at least one of them) Space Marines with the same appearance, but different strategies.
 * Maybe it's representative of two players competing in a game that has both characters; Master Chief's user is a professional tourney player. Or a hacker, irate admin, or a donator on one of those cheesy servers that give special and sometimes gamebreaking abilities to players who contribute money. Hence being able to throw a grenade from being locked down inside of a shield, and deflecting an entire minigun barrage. Doomguy is being controlled by a player that's either new to Doom or a scrub, and therefore doesn't have the skill to take advantage of Doomguy's amazing speed.

Starscream VS Rainbow Dash: How is
 * In-universe, prior to the battle, Rainbow has been given a one-time protection something that saves her from death. Whether it's from a potion or spell (from Celestia, Twilight, or somepony else entirely), I don't know.
 * There is more to a pony than meets the eye. For all we know, for all the damage they can take, they probably have something in their physiology that equines in our world don't have that can protect from the Null Ray's effects.
 * Uh... I'm pretty sure Rainbow Dash isn't electric. Period. So that's why the Null Ray wouldn't work.
 * Organics' brains run on electrical impulses coming and going through the nervous system. That in itself would allow the Null Ray to work on RD, unless you have an idea on what other things her brain could run on. That said, if the guys at ScrewAttack knew it all along, there might indeed be an explanation for this beyond "RD is not electric"; Perhaps RD's body is naturally insulated from whatever effects the Null Ray might have had.
 * In that case, I'd just agree with the below theory about being used to lightning and such.
 * As they mentioned, she's Ponyville's weather manager, so she obviously has dealt with lightning before. In fact, fan favorite Derpy Hooves got hit with a blast of lightning and outside of being slightly charred and shaken, she was fine after a few seconds, which is pretty much what happened when Starscream used the Null Ray.
 * But a null ray doesn't seem to be a "shock" or a surge of electricity like a bolt of lightning, but rather a wave that somehow stops electricity. Although, some Transformers have been smacked with a null ray before, and it doesn't do anything; in particular, it does nothing but piss off Megatron and the Dinobots. Their bodies may just be well-insulated though, which is likely given Megatron's status as an incredible warrior and former gladiator, and the Dinobots being built ridiculously powerful.

Add Death Battle suggestions here

 * T-800 VS Metal Sonic
 * Metal Sonic VS Brainiac
 * A sidekick/brother-to-a-star-chracter battle: Luigi VS …
 * Tails
 * {insert suggestions here}
 * If My Little Pony Friendship Is Magic is gonna have another character selected for a Death Battle, thanks to Season 2, my guess is that it'll be Twilight Sparkle. But what kind of Death Battle?
 * Gifted magicians? Or apprentices to physical gods?
 * A multi-element controller battle: The Avatar VS …
 * Amaterasu
 * {insert suggestions here}
 * Batman VS …
 * Iron Man
 * The Punisher
 * Moon Knight
 * Dante VS Cloud
 * Hellboy VS Ghost Rider
 * Ghost Rider VS Kamen Rider
 * Jak vs Ratchet
 * Mega Man VS Astro Boy
 * Darth Vader VS Lord Voldemort
 * Lex Luthor VS Doctor Doom
 * We already had an 'army-type' Death Battle with the two Mad Scientists. What about a 'team-type' Death Battle. We'll pit the RED Team against…
 * Red Team, of course!
 * Plus Blue Team and Tex = Blood Gulch Crew
 * NOBLE Team
 * {insert suggestions here}
 * Wiz vs Boomstick
 * That's…actually a good idea.
 * If that happened, it would likely be a joke battle, sort of like the "Death Battle T-Shirt VS All Other T-Shirts" battle. They'd probably make up just about everything and argue constantly over the result. Wouldn't stop it from being damn funny.
 * Yuna VS Lucy
 * Unicron VS Galactus
 * The Flash VS Quicksilver
 * Asura VS The Hulk
 * Coyote Starrk VS Xigbar
 * Goldilocks VS BB Hood
 * Touma Kamijou VS Moe Shishigawara
 * Demitri Maximoff VS Dio Brando
 * Rubi Malone VS Revy
 * Bayonetta VS Kurohime
 * Totally Spies vs. Charlie's Angels
 * Indiana Jones vs. Jack Sparrow
 * Chernabog vs Trigon
 * Shao Kahn vs The Lich King
 * Steve VS Captain Olimar