Silicon Surfer said:
Havok with very little skill and holding back severely took down the original version of the Hulk even though the Hulk was enraged. Havoks power has been said by Captain Britain to be of thermonuclear level. The limits of Havoks raw power aren't even known so far as I know. Banshee in his original appearance mesmerized an entire city including the original 5 X-Men. Siryn is at least as powerful and can use her powers in even more ways than Banshee. The Mesmerization effect is potentially enough to defeat the Avenger in and of itself. One of Icemans effects is to drain a target of its heat energy. This can kill any one of the Avengers and possibly multiple targets. Karma can possess one of the Avengers and attack another. Telepaths such as Emma and Rachel also have the ability to attack multiple targets at once. When she was with the Hellfire Club Emma rendered unconscious several of the X-Men even though they had training in mental defense. There is also the mindlock which can freeze an entire crowd and leave them unaware of what is going on for several minutes. Multiple rapid optic blasts from Cyclops could make eunuchs of the male Avengers. Dazzler in her early appearances was capable of briefly stunning the Hulk and increased her formiddability enormously over the years. She can now generate lasers, optic blasts and photon shields .
The only problem with the telepath ordeal is that Iron Man is:
1.) Not affected by telepaths,
2.) Would know that others are, and remove the telepaths right away.
Havok beating an earlier Hulk is kind of powerful, but if you were to count the Hulk of then to the Hulk of now, it's only like beating the Thing, or She-Hulk, both of which can't take down the Hulk on their best day. And thermonuclear is powerful and all, but several Avengers were beyond thermonuclear, such as Jack, Thor, Sentry, and a few others. Iron Man could even reasonably last out a nuclear attack given his armor is in proper repair.
Siryn is easily remedied. She's way too slow for most fliers, and horribly underpowered when considering the same characters. Ms. Marvel would have a field day with her.
Iceman is one of the true threats, and one of the hardest to beat. Thor could concievably do it, as much as any energy user, and Iron Man, since he can keep his armor super heated, and super heat targets too. (Iron Man just can do a lot.)
Cyclops would be a threat. There's little Iron Man could do outside of his sonics, or trying to overpower his beams. Thor could beat him, Wonder Man, Ms. Marvel, and other heavy hitters.
Karma is also a severe threat, but if I remember correctly, she only sends out psionic assaults, so Iron Man has the edge against that, and none of them have the offensive capability to really take on Iron Man. Emma and Rachel would be the largest threats to him. So the order would go like this, Emma goes down before she goes diamond, while Rachel is being fought, then she goes down (probably not by Iron Man, most of the Avengers have the physical power to just take her down anyway), and then Karma, even if she's hiding, is just hunted down while she's absorbing one of the Avengers, and just taken down, reversing the effect. And if push comes to shove, Iron Man could probably extend his anti psi shield to that person and cancel her out.