Steyr IWS-2000 – ★★★★★ Rifle
An absolutely bonkers rifle that you'll want a support squad for. Popularly called IWSxodia. A super high firepower RF with +180% damage, but -RoF. Best paired with the 4 best RoF boosting handguns you can get your hands on. 6 seconds into the fight, her skills kick in and she will basically seem less like a rifle and more like an autocannon, annihilating enemies before her. Doesn't like fighting swarms like Dinergates, but utterly destroy stronger things completely. In terms of raw damage, WA2000 and Enfield can't hold a candle to her. Also useful for blowing up medium sized numbers of very strong yet not-quite bosses. She isn't an end-all solution, but she can get quite close. You can also use her with a reduced support squad, however, you'll want to be sure that you know what you're doing. Since she WILL punish you for using her badly due to the RoF demerit. Also, is MADCORE's waifu.
Her only weaknesses are her low RoF (somewhat mitigated when running IWSodia; either way just don't use her against swarms) and her accuracy – fine by day and against targets with low evasion, but you want someone else for stuff like Gundams (like the Noscope Noodle). That still leaves a lot of potential targets she can handle just fine (on her own or in an FP-buffer setup).
One notable issue with Exodia lineups is the lack of actual hits. In situations where IWS can consistently miss (such as against night armored evasive enemies) IWSodia falls off massively (she only gets so many shots during her skill, and just missing one attack on a 5 link enemy means she needs a second 5x shot on that enemy, wasting all the extra attacks). She is also not-as-good when there are more than a few enemy stacks (even small swarms can be painful).
Furthermore, Exodia lineups suffer massively before the HG buffs go online, and it may be challenging to keep the echelon alive.
While IWSodia is the most notable lineup for IWS, it does not mean that you cannot use her anywhere else. She still does well in a standard FP RF lineup, and performs exceptionally when they don't have enough AP to pierce enemy armor fully. Do note that even in a FP RF lineup, she will reduce your total hit count (compared to 2 FP RFs in the echelon), which may impact performance against certain, more swarmy enemy lineups.
A good unit with a clear drawback. Just don't use her badly.