These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: Twice in Arena: Hadron in the sense that he is just a sooped up normal Robo, in contrast to the earlier fight with Jameson, a mere gatekeeper, who is a Hover Tank with insane defense. By comparison, Hadron is difficult, but fighting him isn't all that different from a standard fight. A completely intentional example is Eddy at the Robocup, as you have been shown to be superior to him already in the events leading up to his fight, and is just a standard fight, no illegal parts or anything.
Game Breaker: Equip the Ray Sky with the Acrobat Pod and Plus One Legs. Use a gun with strong homing and appropriate range for the stage (Thunderbolt, Glider, Homing Star) and a bomb with appropriately large spread or blast (Burrow D, Submarine D, Volcano). Now go to the Dungeon Arena or any level of the Arcade mode and see if anyone can touch you.note Use the Ray Sky's charge to launch it into the air, use the Acrobat Pod twice in succession to launch it even higher, and then, using the two air dashes to stay up there, pepper the arena with bombs and gunfire. At the end of the second dash, use the Acrobat again to down yourself, drastically reducing damage and activating Mercy Invincibility. Wash, rinse, repeat.
Many of the illegal parts can edge on this. Wyrm and Crystal strike stand out.Wyrm is basically a quadruple dragon gun that almost guarantees a downed opponent and the crystal strike renders an opponent completely helpless once it hits. The crystal strike knocks opponents skywards and has no firing lag, allowing you to hit the enemy almost endlessly. If it weren't for the point penalties in the second story mode, the game would be utterly snapped in two.
The sniper rifle in Battle Revolution fires very fast projectiles with a huge amount of stopping power, but leave you immobile for a short while after you fire it. The solution? Put it on a Lightning Sky robo and air dash. Now you can move and fire at the same time.
You can get a similar result with the dragon gun. Or the Wyrm, just to be a huge bastard.
The Jameson with the Sling Gun can grind up and spit out virtually any opponent in Grand Battle mode.
Recycled Script: Arena's plot and and overworld graphics are recycled from a canceled GBA Custom Robo game, hence their primitiveness.
That One Boss: Arena has The two Jamesons, Kindjal and Data Hadron.
The Gamecube version has Rahu, and the fight with Isabella and Eliza immediately beforehand.
The final Rahu fight is a 3-against-1 fight, and even then you still have your back to the wall, thanks to Rahu's absolutely insane statsnote It hits like a truck, is built like a damn wall, has an absurd attack range, has no knockdown recovery period and, despite the fact that it's massive enough that you'd be forgiven for mistaking it for a Metal Grappler, it's an illegal Lightning Sky model, meaning it can freely use its absurdly powerful armaments to bombard you while flying circles around your head. and the fact that it knows that We Cannot Go On Without You. If it weren't for the fact that you have Harry and Marcia helping you out in this fight, Rahu wouldn't have much trouble mowing you down in seconds.