This is how The Mane Six vs. Desghidorah goes in Rebirth of Ryan.
[Desghidorah overpowers the Mane Six with his fire breath from his middle head, his lava gout energy bolts from all three of his heads, his shock pulse, his powerful shockwave, his red electric surge through his bites, and his fiery prye road when he stomps, causing the ground to split open & release flames from within the earth]
[Desghidorah goes after Twilight and puts his foot on her tail. Desghidorah then bites into Twilight's neck with his middle head. He sadistically lifted the now defenseless princess in his horrible middle mouth and bites into her left front hoof with his right head and bites into her right back hoof with his left head and begins sucking all of Twilight's magic and energy out of her, making her become weak]
Rainbow Dash, Pinkie Pie, Rarity, Applejack, and Fluttershy: (together) Twilight!
[Desghidorah continues to suck all of Twilight's magic and energy out of her]