Just need someone to...fight

I will now focus a bit on baddies for the Kaiju to fight.  I am still figuring out the role the aliens play so that will come later. First it will be the forces of the ARC federation.

Both sides of this crazy war are still heavily dependent on the use of Mecha. 
The majority of all the mech used are of the heavy type. Oh yeah just use the science fiction complain walker rules. 

Both sides were working on pushing the envelope to develop super heavy category mech, before the aliens invaded. The Americans were the first to push the boundaries and provide super heavy mech for the ARC Federation.

After aliens and Kaiju entered the arena of war the ARC federation scrambled to keep up. They succeeded.  The Americans not only perfect the Super Heavy class mech. They have created the Titan class mech, metallic behemoths even larger that Kaiju.  These have been nicknamed the Kaiju Killer class.

The Russian and Chinese jointly worked on a way to combat the aliens that greatly affected both nations.

They made attempts at making super soldiers.  They succeed but at a great cost. They tinkered with the genetic makeup of their troops.  They inserted animal DNA, reworked existing human genes.  The results were heavily mutated troops.  Some of the mutations were unreliable but occasionally beneficial. With training and adapting the soldiers were able to harness their mutations. 
The greatest success happened with 3% of those affected by the gene treatments.  Oddly these 3% began excereating a thick oil from their skins that enveloped the soldier and then hardened into a type of chrysalis. After a month they emerged possessing super powers.  As with the others that underwent the gene treatments they were still physically mutated.

While at first the new mutant soldiers were viewed with fear by the masses of the ARC Federation.  That was until a team of super powered mutants successfully stopped an advancement of aliens. Then when that same team managed to take down a kaiju.
These mutants are now accepted and celebrated.

Crunchy bits.

So for mech use the science fiction companion for walkers. Rely on heavy and lower Mecha for the bulk of the troops. Super heavy are common but not the bulk of the army.  The Titan class are new and still quite rare. When one shows up the Kaiju know they are in for a fight.

For the mutants create using Just Insert Imagination's Mutation Deck. What you don't have it.... you need to fix that. It is an amazing product. Here is a link just buy it okay.

http://www.drivethrurpg.com/m/product/190609

For the Super mutants create them using the super powers companion, using 45 power points.  Each mutant has the distinctive appearance hindrance with no benefit.  They can also take the alien form hindrance as their major hindrence.

So that should cover the ARC federations forces, well at least the basics.