Disccusion - Viability of Geigeroach

[Lord Windos]

And what a fine first post you made, mate! Geigeroach isn't my favorite natural Nuclear type (That would be Xenoqueen!), but I always thought it was a decent Pokémon that had potential. Now, let me critique your set, mate!

- As it stands, Gieger is a niche pick along side Soundproof Para, Hazma, and Specially Defense Garaweal as point checks/counters to the green demon. Problem with it over them is that its particularly weak to HA Fire unlike the other of those three, and doesn't have the same sheer strength in STABs as they do (Hazma has Expunge, Para. has Boom Burst, and Garaweal has Iron Head [Which target's Nuc's weaker Defense stat] with/without Sheer Force). It is, however, faster than all of them, and access to Overheat too boot, so it still is able to compete against them all.

-Proton Beam has minimal drawbacks on a Choice Set, as you are likely going to be switching out ASAP after firing one off. Life Orb sets would be better with Gamma Ray for consistency, while with FS it doesn't really matter which Move you use, so long as it uses it at some point.
-Heat Wave/Flamethrower can be used over Overheat on LO sets if you want it to maintain effectiveness without being forced to switch, and/or if you want to make a Nasty Plot set.
-Infestation is also an option if you want to try and trap Nucleon or whatever switches in its place to prevent an opponent from double switching/ease up on prediction. Alternatively, you could run Signal Beam in its place to chance its nature to Timid, and simply nail whatever comes in if you have plenty of U-turn support. Works well on a NP/Choice Set too.
- Knock Off could be ran in the forth slot to cripple any Pokémon switching in on, which will most likely happen often. Explosion and Flail, on the other hand, can severely cripple or outright KO weakened Pokémon, and the former lets you gain momentum if Gieger is no longer useful/isn't useful against a particular team. Those moves work best on a Focus Sash set, obviously.
-Since this thing is designed to counter Nucleon, you should choice Mild or Modest, as the former lowers its already decent Defense (Which doesn't matter against Nucleaon), and the later allows you to more easily KO it. Gieger isn't going to outspeed Nucleon in any scenario unless Sticky Web is out and it has a CS, so a speed boosting nature is not needed necessarily.
- Priority attacks will be the bain of your existence with this guy, and its very easily revenge killed. Its also highly suspectible to being Pursuit Trapped, which M-Arbok, Chainite, and Oblivicorn excels in. Chainite in particular can perma trap it with Shadow Tag, and then threaten to KO with Shadow Sneak.
- In order for Gieger to work well, it needs heavy team support. Hazard Cleaners area must on Focus Sash sets, and having at least one other U-turner/Volt Switcher to work in tandum with them is recommended. If you are planning to sweep or safely switch them in, you probably need another Sticky Web user, or a Pokémon with Intimidate/Petrify that will force switches.
-The only other sets I can think of for Geiger is suicide lead, Choice Scarf, and Nasty Plot sweeper. NP would need even MORE team support, CS is outclassed by Nucleon, and Suicide Lead defeats the purpose of it being a premier Nucleon counter.
-Strong Special Walls can counter anything other than a Nuclear Move without prior damage to them, and Magic Bounce Users like Mega Sableye can ruin any attempts to gain momentum with support Moves.

Overall, I think you did a fine job with this Giegeroach set, but you need to consider more about how counterplay and Revenge Killers/Trappers can hinder its efforts. That, and S51-A isn't just a Nucleon counter, but is in fact the best Hazard Cleaner and one of the most flexible Pokémon in the metagame, so Gieger wouldn't be able to totally invalidate its position on teams. Coalith is pretty much the alternative for it if a person wants a faster hazard cleaner, particularly if they run Chlorophyll and are on a sun team, or just Levitate.

EDIT: Also, Bug resists Ground to my knowledge, so at least Gieger can takes neutral hits, unlike Garaweal. And Hazma can also work as both a Nucleon Counter and Hazard Cleaner, if you need role compression and can afford to run it.