Well since people here have all been talking about Godzilla vs Slattern or vs King Kong I figured why don't we expand a little?
Combatants:
Gipsy Danger vs Sachiel (Rebuild)[]
Yes, it's the famed Gipsy Danger against Sachiel, the Angel of Water from the series Neon Genesis Evangelion, able to create lances of energy from its arms and fire energy blasts from its eyes and while not much in terms of melee, is able to instantly "bulk up" to increase its strength.
Striker Eureka vs Destoroyah[]
Striker Eureka, the first and only Mark 5 Jaeger ever produced by the PPDC against the demonic Destoroyah, who could possibly be Godzilla's most powerful enemy of all time.
Cherno Alpha vs Kalros[]
Cherno Alpha, the sole surviving Mark 1 Jaeger and oldest one still in service against Kalros, the massive "Mother of all Thresher Maws" that's been around since ancient krogan civilization. With burrowing abilities, acidic spit and massive claws, she was able to easily take on and defeat a Reaper.
Slattern vs Reaper Destroyer[]
Slattern, the first Category V kaiju the Precursors have created as the first of many to exterminate humanity versus a Reaper Destroyer, a smaller (160 meter) model of the infamous synthetic race that has been exterminating galactic civilizations every fifty thousand years for at least a billion years.
Leatherback vs Evangelion Unit-01 (Rebuild)[]
The gorilla like brute featured heavily in Pacific Rim's commercials taking on the iconic being Unit-01 with its vast arsenal of weaponry that could happily be at home mounted on a Jaeger, from giant vibrating combat knives to building sized rifles, Gatling guns and rocket launchers.
Slattern vs Biollante[]
Slattern against Biollante, a kaiju that's as massive as she is unique as she is a rose-Godzilla genetic hybrid that can shoot out radioactive acid that can dissolve diamond and countless vines that are either sharp and strong enough to actually impale Godzilla or venus flytrap mouths that spit up more acid.
Mutavore vs MechaGodzilla I[]
Although Mutavore didn't even get a minute of screen time in the film and its only accomplishments are walking through a wall and getting its ass kicked by Striker in the span of only a few seconds, was said to have easily trashed a Mark 4 and a Mark 3 Jaeger in the novels. Can it stand up to a mechanical monstrosity from space that actually gave Godzilla a run for his money?
All Pacific Rim Kaiju vs Zeruel (Rebuild)[]
This time it's all the Kaiju prominently displayed in the movie: Trespasser, Knifehead, Onibaba, Mutavore, Leatherback, Otachi, Raiju, Scunner and Slattern. Can their combined might take on the dreaded Angel of Strength, Zeruel? My apologies, but it's just that Zeruel is just too awesome for me to really explain with words.
Knifehead vs Guiron[]
Guiron, one of Gamera's first foes, and is quite possibly the original knife headed kaiju in the entire genre. He is the guard dog for a dying alien race to fight off a Gyaos swarm and for some reason Guiron is able to shoot shuriken out of his face.
Raiju vs Voltron[]
I'll be honest, I don't know anything about Voltron here...
Otachi vs Ghidorah[]
The king of terror and destroyer of worlds himself, Ghidorah was the first of many extraterrestrial kaiju to make an appearance in the Godzilla franchise. Being Godzilla's most well known, and the one that appears in more films than anyone else (with the exception of Mothra).
To be updated