The last video game boss you've defeated is now in Ponyville.

[mrmistermistermr]

Dire Miralis from Monster Hunter 3 Ultimate.
I'd say they're pretty screwed without a good ice weapon.

Spoiler: show

[Blode4]

Cletus from Chaos on Deponia, if that counts as a boss. There is absolutely danger with him.

Also Ninja Sue, Possessed Misery, and the Undead Core from Cave Story. Quite a bit more danger there.
Post Merge

Hydra in Kingdom Hearts 2, yep their dead I could barely beat him.

They'll definitely be screwed, since they won't have Phil to tell them, "GET UP ON THE HYDRA'S BACK!"

[AaronMk]

Well, lessee... We got a heavily augmented black-ops soldier with cloaking abilities and I don't know if Ponyville has ever heard of EMPs. A duel machine pistols.

I'm sure it'll go down as Bloody Sunday before someone hits the auto-fix button.

[HunterOfTheDark]

Who's been messing with time? The Dahaka has destroyed half of Ponyville trying to find the culprit.

[S_Realm]

Um, the BBB (Big Blue Blob) would like a word with the unconquered uncolonized lands of Equestria.

[Verdant Tome]

Uh, bosses?
I don't know many bosses
I haven't played games with bosses much
Do Punch-Out characters count as bosses? No?
What about LoE dragons? No, that'd just be redundant, there's already one there.

I guess the last true video game boss I ever fought was Ballos, the True Final Boss for the best ending in Cave Story.
He's gone mad with his own magical power and rules the game's variant of Hell.
Here's some pictures of what he looks like in his various forms. Might be kinda creepy towards the end! Don't look if you don't like creepy, or are playing Cave Story and don't want boss spoilers (besides the ones I already gave - sorry about that)

Spoiler: Normal Appearance/Stage 1 • show

Spoiler: Stage 2 • show

Spoiler: Stage 3 • show

Spoiler: Stage 4 • show

Have fun, Ponyville!

[Chromastone64]

The final boss of Lightning Returns: Final Fantasy (DO NOT CLICK IF YOU HAVEN'T BEATEN THE GAME!!)

Spoiler: show

 [ Invalid YouTube link ] They're going up against God. But he IS killed by the bonds of friendship...they have a bit of a chance!

[MrSpyro]

Evilized Kaos from Skylanders. You had to give up the Elements of Harmony, Twilight, 'cause Now Equestria is pretty much screwed.

[HunterOfTheDark]

Oh crap, Vanitas is here. Now there's a bunch of Unversed running around the place because of him. Have fun Ponyville!

[LunarDusk]

Albedo from Xenosaga episode 1.....yeah ponyville is so doomed

[Sakura_Blossom]

Omega Ridley From Metroid Prime 3....

Yep, it isn't going to end well XD

[TwilightNight]

Not sure if this counts as a boss, but I faced Resetti from Animal Crossing and came out alive?

It's either that or an 'unknown disease' from Oregon Trail...

[Chibalt]

The Rotten from Dark Souls II, yeah they should be pretty fine.

[HunterOfTheDark]

Gertrud from Puella Magi Madoka Magica Portable.
Ponyville will be fine, all they need is some pesticide and they'll be good to go!

[Blue Shield]

Legate Lanius... Fallout New Vegas... O.O

[Verdant Tome]

Uhhhhhhhhhhhhhm... a Pinger from Crysis 2. Eeep.

[LunarDusk]

hmm..Giygas from earthbound...yeah we all know what would happen next

[ChristaMoose]

...
ZOMG from BTD4. Well I guess they are safe as long as they have those needles... and a LOT of stamina.

[Zsaszz]

Mmm...the Alpha-Ceph from Crysis 3, I think that they're pretty much doomed, unless they have a pony that can use a Nanosuit.

Spoiler: Prophet • show

[GoldenTerrabyte]

Metal Face from Xenoblade Chronicles...





DOOOOOOOMED!!!!!


Not that he was super hard to beat, but the fact that the Monado and two other people helping with heavy weapons which were needed to take him down, it's impossible for him to be beaten here!