This is either Knuckles fighting Rouge, or Rouge fighting Knuckles.

1) You might say that this opponent is 'suitable'.
Cos of Rouge's attire perhaps? With the heart and all, and that's a suit in cards.

2) Its good to be
bad
Rouge is the Dark side Story character

3) Clench fists tight become more redder
If I fight Eggman, Rouge, whoever

4) ...And I
thought only balloons went up with hot air.
The floor opens and blasts hot air and sends you both up to the scaffolding.

Way to go SS! Yes, the boss in question was KNUCKLES from Sonic Adventure 2. Aint I a stinker =D

The correct clues are as follows:

1) You might say that this opponent is 'suitable'.
The track that plays in the fight is 'Suitable Opponent'. Track 10 on "multi-dimensional Sonic Adventure 2 OST (DARK side disc)"

2) Its good to be bad
You control bad-bat-girl Rouge during this fight.

3) Clench fists tight become more redder
Lyrics from the Sonic Adventure 2 version of Knuckles' theme, 'Unknown from M.E.',

4) ...And I thought only balloons went up with hot air.
Indeed, the intense blast of hot air from the tower's floor opening sends both characters up the scaffolding.

Okay, batter up.

Alright, let's see...

1. His drill won't pierce the heavens.
2. This boss is good at restricting your freedom of movement.
3. Sonic didn't have to put up with this.

This one should be pretty easy

Marble Garden, Eggrobo non-airborne drill fight. ^^

KORREKTO TEETEEJII

"Corackto Titagee"

*kicks babelfish*

"、カメの人訂正しなさい" ?

Anyhow, bosstime.

1. Ovoid Onlooker.
2. Ride the deadly delicate acrobatical dance.
3. Hey, don't I do this again later?

Dammit, Yuku.

Egg Hawk, or whatever its name is, the first boss in Sonic Heroes?

nope.

Wing Fortress Zone's boss?

Yessir.

OK, here we go then.

1. Don't worry! I'll save you!
2. You can't attack this boss directly.
3. Explosives? Again? Really?

Its going to be wrong, but I'm going to say its ZERO, Amy's only boss in Sonic Adventure.

1) This is what makes me unsure, but wasn't she protecting Birdy or one of the other Flickies?
2) The Piko-Piko Hammer does do any damage, but you can knock Zero into the electric barrier to deplete its life gauge.
3) Er.. it uses explosives?? (its been a long time since I could be bothered to play Amy's Adventure, so I've forgoten most of this fight)

It is wrong indeed this time, sorry. :3

I'm going to take a stab here and say E-105 Zeta from Sonic Adventure.

Surely those clues count for any of the E-Series 'bots that Gamma fights.
Ghah! Is this going to be a boss from Sonic06? 'Cos I haven't got a chance...

Unless... could it be the first Eggman boss fight as Tails in SA2?

Everyone has headed in the wrong direction thus far, so I am going to add another clue.

1. Don't worry! I'll save you!
2. You can't attack this boss
directly.
3. Explosives? Again? Really?
4. Barnes Wallis would be proud.

*googles Barnes Wallis*

?
EDIT: Actually, I'm going to take another guess and say the Hot Mobile boss from Lava Reef Act 2, Sonic & Knuckles.

The boss of Volcano Valley Zone?

Both incorrect. I may need to add another clue at this rate.

i'm bad with these things ... .but i'll try anyway.

the egg dragon boss from the sonic episode in sonic 06, i'm guessing the one sonic was trying to save is the princess.

The Egg Wyvern, you mean?

Wrong again.

1. Don't worry! I'll save you!
2. You can't attack this boss
directly.
3. Explosives? Again? Really?
4. Barnes Wallis would be
proud.
5. It's possible to beat this boss without the need for more than a single jump.

Underground Zone boss from Sonic 2 gg/sms?

1. Don't worry! I'll save you!

Sonic is about to fall into a lava pit when eggman comes to the rescue... for whatever reason.

2. You can't attack this boss directly.

Indeed.

3. Explosives? Again? Really?

He shoots spherical bombs at you.

Reference to some boss in Sonic 1 sms/gg? Jungle Zone or whatever.

4. Barnes Wallis would be proud.

*googles* "He is best known for inventing the bouncing bomb" (from Wikipedia)

The bombs bounce before exploding.

5. It's possible to beat this boss without the need for more than a single jump

By quickly dodging and crouching you can dodge the bombs, but at the end you need to jump to dodge the eggmobile.

Erika gets it in one!

Too lazy to think of something, someone else do this for me (except SilverShadow). =w=

Khyaah~! Dammit, SS! You're so mean! I hate you! (Actually, I hate myself more for not getting it myself TT_TT)

Anyway, while I'm here, I might as take this round out of your hands, Erika.

1) Grh! Its too high! I cant reach!
2) Didn't your mother tell you that jumping on exploding bombs is dangerous?!
3) That's right... come down so I can get a good whack at you.

Hydrocity Zone boss?

Oooh~! Close, but not quite.

Carnival Night Act 2 Boss.

Rapidfire was warm. Your getting colder, Jeff.

Gigantic Angel boss from Sonic Pocket Adventure?

DING-DING-DING~!

You got it!
I do have to apologise to Rapidfire who few into my heffalump trap - it was my very intention Sorry n__n;.

All righty, give me a sec here...

1. Attack of the (mini) Clones.
2. Rayman, eat your heart out.
3. Is that Chaos Control?

Sonic 2 MD Death Egg final boss?

Nope!

I think I'll go another four guesses before I give another hint.

Too easy! Piece of cake! - as Sonic would say. In fact, the hardest part was remembering the damn thing's name XD
Yeah, its Dark Guardian from Sonic Unleashed.

1. Attack of the (mini) Clones.
It sends out little drones to mess you up. They fail.

2. Rayman, eat your heart out.
You fight this boss as the Werehog, who throws his punches in a very Rayman-esque fashion.

3. Is that Chaos Control?
It has it's little teleporting trick to confuse you. The Werehog my be ugly, but he ain't stupid.

Negatory- great guesswork, though! To be honest, I hadn't even THOUGHT of the Dark Guardian when I wrote those clues, so I wish I could give you a consolation prize for sound logic despite the incorrect guess!

Three more 'till the next clue.

NOOOOOO! MY PRIIIIIIIIIDE!!

I imagine this is probably wrong, but: Doomsday Zone boss?

Nope!

Now, let's see- two more before I said I'd give a hint, right?

Screw your rules! I want that extra clue NOW!

Ah, well, I guess I may as well.

1. Attack of the (mini) Clones.

2. Rayman, eat your heart out.

3. Is that Chaos Control?

4. Slow down, hedgehog!

I had to look it up, but I think its Mecha Gorilla from Sonic Labyrinth.

1. Attack of the (mini) Clones.
Battle begins with little robot monkeys

2. Rayman, eat your heart out.
He shoots his arms out at you.

3. Is that Chaos Control?
He only appears after the wave of little monkeys.

4. Slow down, hedgehog!
The whole game features a slow Sonic.

If this isn't it then this is totally not fair TT_TT

If I ever get it again, I will pick one from Tails Sky Patrol.

In order to keep this topic going, I'll just say Blue, just go.

Aww. I only win by default? (sadface)

1) So high up! And here's me without a floating platform.
2) What, so he's just gonna go back and forth. Okay I guess tha-- HOLY CRAP A SPIKE!
3) O-kay~, runnin' outta footroom here!

Easy.

Spring Yard Zone, Sonic 1, Mega Drive/Genesis.

Marble Garden Act 2 - Sonic and Tails.