are we covering all sets, cosmic cheap, cm, or the lo attacker set?
edit: omg wrong pokemon, I thought sigy was the thing to counter lol
edit 2: wait, no, i'm confused now, what is it that we're covering currently?
Sigilyph is the Pokemon we're covering in victim of the week at the moment, all sets should be covered, although you can mention some checks and counters that only beat specific sets as long as you make that clear.
Alright, to start off this discussion, i'm going to cover a few ways to cover
Cosmic Power Sigilyph, the absolute bane of most new players. Despite the fact that it often gives new players trouble, i don't really ever have that much trouble with it (i actually find it to be the worst sig set lol), it might seem imposing at first but there are multiple good ways to keep it in check, some of which i'll be listing below to try and help out any new players viewing this thread.
Dark-types with recovery of any form, such as Spiritomb and Mandibuzz: Since Cosmic Power Sigilyph relies on Stored Power to deal damage, leaving it completely vulnerable against Dark-types bar a Psycho Shift Burn, Pokemon such as Restalk Spiritomb and Mandibuzz are able to handle Sigilyph rather reliably. Not being able to be hurt by Stored Power, being able to recover off the damage from burns, and in the case of Mandibuzz being able to use a combination of Taunt and Whirlwind to phaze and completely shut down Sigilyph for the time being. These Pokemon are probably some of the best/most reliable ways to deal with Cosmic Power Sigilyph (they perform well against other sets too).
Trick: Although it means getting handed a Flame Orb in return, Trick is one of the easiest and most effective ways of crippling Cosmic Power Sigilyph for the rest of the match imo, and its usually my go to method if i can't fit something like Restalk Spiritomb on my team. Sigilyph takes a really long time to boost up enough for Stored Power to do some serious damage because of its incredibly low 20 Base Power early on, meaning a Sigilyph without any boosts isn't much of a threat at all, especially when its locked into a move and can't set up at all in the future, let alone spread burns or use Roost to recover. A tricked Cosmic Power Sigilyph is pretty much dead weight for the rest of the match. Pokemon such as Manectric, Rotom-C, and Rotom-N make good users of Trick, and have a STAB super effective Volt Switch to boot!
Haze Cryogonal: Haze Cryogonal is a reliable and effective way to deal with Cosmic Power Sigilyph on more defensive teams. As mentioned previously in the Trick section, Sigilyph takes quite a bit of set up to become a huge threat, as its Stored Power is incredibly weak beforehand. Cryogonal takes perfect advantage of this and uses a combination of its recovery, special bulk, and haze to just completely wall CP Sigilyph. Its really hard if not impossible for Sigilyph to PP stall Cryogonal as well, because Haze has an absolutely massive amount of PP to work with (Cryogonal can haze more than Sigilyph can set up Cosmic Power lol).