Armor Knight G (Grand) Kaiser a.k.a. Kikaioh
A Mazinger Z Shout-Out, meaning it comes with a paired Rocket Punch, a Chest Blaster, and a navel-launched bomb. Its Final Attack involves a BFS and a lot of spinning. Known as Kikaioh in Japan, thus the title character of the series. Piloted by the Hot-Blooded Junpei Todoroki
The Messenger of Beauty and Justice Diana-17
The sole Fem Bot in a field awash with Real Robots, giant aliens, and Super Prototypes. It's fast, equally comfortable fighting on the ground or in mid-air, and can hurl a very damaging Energy Ball to finish its nasty ground to air or air to air combos. Bonus points for its control system and the combat suit of its pilot Reika Amamiya, which seem to be a nod to G Gundam.
Magical Patched Robot Bolon
It's the kind of giant robot you'd least expect a Magical Girl to pilot. Possibly based on the Boss Borot from Mazinger Z, this robot appears to be cobbled together from a water tank (torso), a power shovel (right arm), a wrecking ball (left arm), a boat and what appears to be a bus (feet), and a house for the head, among other things. The odd assortment of parts doesn't detract from its ability to fight, though. Piloted by the Magical Girl Polliam "Pollin" de Pollinten, who has a huge crush on Junpei, and is perfectly willing to fight the other female pilots over him... whether they're interested in him or not.
Strategic Variable Fighter Rafaga
A Macross Variable Fighter in all but name. Armed primarily in its humanoid form with a beam rifle that doubles as a club, missiles, and a punching super move that sinks its fist deep into an enemy's torso, it can optionally equip 2 shoulder-mounted energy weapons and a heavy projectile cannon. Its alt forms give it 2 extra supers: bombs from above and a multi-hit tackle. Rafaga's main pilot character is Simon Harvard (a Composite Expy of Roy Focker and Max Jenius), although Simon's wingwoman Amuritta (Expy of Claudia La Salle) is available as a secret character.
Super Defense Armour Dixen
A mixed Gundam Shout-Out, it has a Laser Blade, a beam rifle, bazooka, shield, a shoulder-mounted BFG, and remote-controlled beam cannons. A certain power up allows Dixen to pelt the enemy with homing lasers. Can be piloted by either Nakato Farland, whose story is a Gundam pastiche, or by Halma Frockheart, whose storyline is more like Gunbuster A variant piloted by Shadow Red is available as a secret character.
What's an Ultraman clone doing in a Humongous Mecha fighting game? Proving to players that you don't need to be mechanical to kick robot ass, that's what. Armed with punches, kicks, energy rays, and the ability to ignore the laws of physics, Pulsion manages to Shout-Out to Neon Genesis Evangelion as well, with its possible arsenal of double-bladed sword, thrown lance, and a combat knife. Let's add the fact that it can go all out in a bestial manner... Pulsion's civilian identity is either the male human alien Kai Kaines or the female human alien Kei Keirum A variant called Dark Pulsion, controlled by an evil Kai, is available as a secret character.
Phantasm Unit Twinzam V
Getter Robo minus the tracked, heavily armored, underwater combat form. To make up for it, it is given 3 super moves, one for its Fire Formation, another for its Plasma Formation, and one that acts as its Transformation Sequence. That's right, it changes tactics and weapons to the tune of a damaging Pillar of Light. It has two different finishing moves, one of them a Shout-Out to Voltes V and the other one possibly to Combattler V. Piloted by the Yumeno siblings, Daichi Yumeno and Sora Yumeno.
Heavy Armour Tank Wise Duck
Word Of God states that this tank with arms and legs is a nod to the HWR-00-Mk. II "MAC-II / Monster" Destroid from Macross. It is equipped with a claw on one hand, a pile bunker/BFG in the other, missile launchers on its shoulders and more on its back, and a three-barrelled autocannon mounted between the legs. It can lay mines, equip flamethrowers and artillery, keep an enemy at bay with ranged attacks or lay down a punishing barrage of melee attacks. The one thing it can't do is jump. The Wise Duck is piloted by a crew of five: Gonzales, Arvin Clauford, Ricky, Thomas, and Herman. A variant (complete with Zeon-style commander's antenna) piloted by Shadow Red is available as a secret character.
Maryou Shogun Gourai
Your basic Ace Custom mecha for The Dragon: blood-red, BFS, and the fact that it holds a strong assortment of sub-weapons and brutal fighting techniques. Piloted by the masked Shadow Red, whose real identity is Mamoru Todoroki
Variant Armor Blodia II Custom
The only secret character that's not a Palette Swap, this Guest Fighter comes from Capcom's Armored Warriors/Powered Gear and Cyberbots games. Piloted by Jin Saotome, whom most western gamers may recognize from Marvel vs. Capcom.
A one-eyed yellow brick castle-like golem. (In)famous for its sweeping Eye Beams, and the fact that its basic melee attacks hurt a lot. Piloted by the Egyptian-themed alien Arekshim.
A huge, floating weapon of obviously alien origins. Piloted by the android girl Yale.