Iron heart surge

"Instantaneous effects can’t be removed by iron heart surge. However, any effect with a duration of 1 or more rounds, including permanent-duration spells or effects, may be removed by iron heart surge, nor does iron heart surge restore damage or ability drain. Iron heart surge doesn’t replace lost levels (though it would remove any negative levels resulting from a single spell or effect). It would neutralize a single poison coursing through your system, or a single disease that afflicted you."

– How IHS works according to Sage

The Iron Heart Surge is perhaps the zenith of Weeaboo Fightan Magic ignoring common sense for the sake of being "cool." It is more-or-less exclusive to the Warblade class.

Iron Heart Surge can do this because of some of the most spectacularly bad wording prior to the inception of the Pyrovore. It was intended to copy the age-old anime move where the user yells and flexes their ways out of a bind. The problem is that IHS is a maneuver, something you need to be able to take a Move Action for. And if you're, say, tied up, paralyzed or stuck in a web you cannot move and as such cannot use IHS. But because of its wording it can do a lot more than intended...

The IHS lets you pick any ongoing effect or condition affecting you and end the effect. But like Thanos' Reality Stone, the limitations are so vaguely defined that it's incredibly overpowered in practice. Because of the particular wording, it could be argued that "sunlight" is an effect, just to give an example, allowing you to stop the sun from producing light. Instantaneous things like fireballs and one-time damage cannot be targeted, but as long as it lasts longer than one turn (including permanent effects) and does not stop you from moving you can end the source of something bad happening to you. This means that if you're caught in a blizzard that deals cold damage over time or in a desert which hurts you to dehydrate, all you need to do is a good old Iron Heart Surge and the blizzard vanishes and the desert no longer deals heat damage. It can also be used to remove poison or disease ("Yes, Timmy. It's your fault that you're dying of cancer at age seven. You should have dipped Warblade") but negating Antimagic Fields or Cloudkill spells is nothing short of bizarre.

It can even alter effects such as being blinded by the the sun: look into it, use IHS and BAM! Sun's gone. Fell into the ocean and started to drown? IHS and BAM! Ocean's gone. Make sure to bring something that mitigates falling if you do this. Go to the Elemental Plane of Fire and start taking fire damage? IHS and BAM! Fire's out. Also, remember that aging is arguably an effect, and that you can thus remove the concept of time from existence.

Some argue that you can also use this to kill monsters with: get swallowed whole by a Purple Worm, get dealt ongoing acid damage, use IHS and BAM! Purple Worm's gone (though a smart GM would argue that only the acid disappears). Force-feed yourself to the Tarrasque and FLEX YOUR WAY INTO LEGEND. Abbreviation 'IHS', is incidentally also a Christogram - implying that you're FLEXING WITH THE POWER OF JESUS CHRIST and not your own.

/tg/ talks about IHS and how to abuse it

This likely would have been smashed in errata... if Tome of Battle had actual errata. By the point errata came along for Tome of Battle it was clear Wizards just did not care about 3.5 anymore so the published errata for Tome of Battle just ends in the middle then becomes a copy of the errata from a completely different book.

Dreamscarred Press's version of Tome of Battle for Pathfinder, Path of War, has two versions of Iron Heart Surge: Sanguine Perfection and Temporal Body Adjustment. These differ enough they actually makes sense. Firstly Pathfinder actually defines "condition" as a narrow 34 items, with Path of War adding a few more. Secondly Sanguine Perfection goes one step further and only lets you nullify a white list of certain conditions while Temporal Body Adjustment is from an explicitly supernatural discipline based on time manipulation. Thirdly they only nullify the effect on you, not ending the actual source.

No fun allowed

The exact wording of this ability is as follows: "When you use this maneuver, select one spell, effect or other condition currently affecting you and with a duration of one or more rounds. That effect ends immediately." The text does not say anything about purging the source of said effect, just ending what is applied to you. It's pretty clear that this does not allow you to blow up the sun by ending heat stroke or destroying the Tarrasque from within. If you use it to purge yourself of the effects of cloudkill, heatstroke or freezing to death, you'll just get struck with it again just by being in the vicinity (Though you could use it to get a reroll to your saving throw).