Frankly, I don't know how you guys like this boss. I have two major complaints that pretty much wreck this boss.
First off, it's boring as
shit. Here's how to win the first part; stand on a corner, and jump in place. If Iron Sonic does his bunny hopping, you'll land on him. If he crawls on the floor, go to the other side of the room and jump there. And during his missile attack, just run to the other side of the room, jump in place, and then jump to the opposing side of the room. This is just incredibly dull and solved in about a minute, but executed in about 3.
After that, the boss becomes really easy after his first attack. Just stand in the middle, walk or spindash jump to the safe zone, and jot back to the middle. His diving attack is easily the stupidest as not only is it the easiest to avoid of all his attacks by far, it's also the attack with the longest "here, come hit me" time by far. It's like he doesn't even care at this point, which the player probably doesn't either.
This boss, while not Eggmobile again, just feels really basic and seems to get a mild pass for the 2D level novelty. It really feels like a boss you face far, FAR earlier in the game, only with obnoxious vulnerability time, which leads me to my next issue...
Second, your bosses just feel like they go on
forever. This is something that has plagued all your bosses. Your bosses take 8 hits to kill, as per standard Sonic rules, but use 3-hit-kill boss vulnerability frequencies. What do I mean by this?
Your boss seems to do the same thing that most Modern Sonic bosses do; do an attack for several seconds, and then go "hit me", and then select another random attack to do. Sometimes the bosses do other attacks before being vulnerable or something, but usually, that's all they do. While kind of dull, you usually finish off the boss before this sets in because they have less hit points than 8.
Now, take almost any boss from a 16-bit era Sonic game (the exceptions usually being final bosses or the more gimmick-y ones). They usually take 8 hits, and you can hit them
more than once. You can often hit them mid attack if you risk it and don't take long at all. Even some final bosses like the Death Egg robot (either the 2 or 3&K ones) take multiple hits and allow you to do more than one strike at the given moments.
Iron Sonic does the worst of both worlds, and then some. He has very low vulnerability time unless you know where he'll be long in advance (and you very well can, though I wouldn't doubt this being intentional), but you gotta wait through this really dull process of doing the same ridiculous bunny hop or rolly polley across the floor like a giant infant, and THEN you can hit him. It stops being a boss and feels like a chore. Its barely any better than waiting for those stupid shields to go down.
And like I said, he just stops giving a fuck after his pinch. He does his
AoE attacks, and then then does his silly little ground pound which he yelled to you about the whole way, and concludes by laughing in your face for a half hour while you go stomp on it.
Iron Sonic desperately tries to ape its older brothers Silver Sonic and Mecha Sonic, but just isn't anywhere near as interesting as either. Silver Sonic had the benefit of "
oh shit I have no rings", but his only real surprise was the "shoot needles" attack. Mecha Sonic was a far better Silver Sonic, having many more moves and even getting an extended movepool in the Knuckles boss fight. And even after
them, we have Gmel, who in his last normal fight is closer to Silver Sonic, but has teleporting, and his missile attack is slower but slightly more effective, but even then, he was just a miniboss before the REAL final(ish) fight.
Iron Sonic just doesent feel as interesting as any of these guys. I don't know about Gmel, but the Silver/Mecha Sonic pair both tried mixing up their spins to throw you off, like jumping really high or Mecha Sonic's backdash. Neither of your two movement options do anything. Like I said, they're easily thwarted and even then, arn't very different in how you avoid them. Using the 3D to shoot from the back seems interesting but is no different than dodging Eggmobile missile spam. The crushers during the pinch seem ok, but they just don't have much going for them after you dodge them once. And finally, his ground pound just doesent have any extended hitbox to help it, like Death Egg robot's massive size or Gmel (toy kingdom boss) exploding upon impact for a blast radius.
To be far, this boss isn't TERRIBLE. It just isn't what I'd expect from a boss THIS late in the game, or even a midboss. It's like something you throw into the 2nd or 3rd level. A simple set of easily predicted attacks. Really anticlimax for the final level. But it isn't an Egg Mobile clone so... that's something.