Considering there are only 4 spikers in gsc (Forry, Cloyster, Qwilfish and event Delibird, not counting Smeargle) saying "one of the better spikers" isn't really a big achievement. I will just go so far and say that Qwilfish and Delibird are completely unviable in the gsc ou metagame and therfore only compare it to Cloyster. There was a thread about gsc forry on here not long ago so i guess i will just sum up the main points of it. Forry has a couple of things over the more used and arguably overall better Cloyster - spin+explosion, a toxic immunity, a bigger longlivety against most Stall teams, Stab hidden power bug to hit Starmies trying to spin on it, it doesn't get ohkoed by thunder missy/gengar, takes neutral damage from boltbeam and is therfore a decent stop to nidokings, gengars, dragonites, and due to physical bulk it can be a stop to things like heracross and mono normal attackers (i will say something about that later, so wait before you type that it's setup bait).
The set Crestfall posted is in fact what most forrys look like, but it does have an actually broader range of options. Reflect and Curse help it stall out physical attackers, +6 lax versus +6 forry will always end in a pp stall, unless someone gets lucky with crits. Hp Bug got already mentioned, Toxic is pretty obligatory too, which can help winning the spikes war in the long run versus Cloysters very effectively since they usually lack rest and versus Starmie somewhat effectively. Giga Drain is an option that hits Cloysters very hard and forces the Cloyster to switch out. Hidden Power ghost can hit Missy or Gengar coming in to spinblock it. Hidden power electric is an option as it hits Cloyster too and additionally grants a 4hko on Skarmory, even though you might just be better off using hp electric Cloyster when you want to go that far. Hp fire actually 2hkoes opposing Forrys, but outside of that it is pretty much a waste of a moveslot. Considering that Forrys usage is not very high generally i don't think it will be worth it most of the time.
Forry has one huge problem - fire moves. And gsc is a meta where everyone and their mother can run a fire coverage move, even fucking Machamp runs Fire Blast sometimes. You will often have to play very hesitantly with your Forry to scout for fire moves if you don't want your spiker/spinner ohkoed early.
Forry only works on spikes based teams, because well, that is it's main purpose in life. You are using a whole mon dedicated to it, so make use of those spikes. If your team is not strictly centered about Spikes you might as well use Cloyster instead, which has way more offensive presence. Mons that work with it: Suicune, Rhydon, Ttar (phazer, can come in on fire blast lax), Raikou (kinda self explainatory, absorbs special hits, phazes), Missy (best spinblocker).
In case that isn't enough on gsc forry you can just look up the thread, it's still on page 1.