Something I noticed when reading Delta Noctowl’s wiki page is that it learns Sheer Cold and has No Guard as its hidden ability. This is a terrifying combo; we were worried Machamp might have gotten it after the gen 1 transfer, and it only has 55 base speed; Noctowl has 70 base speed. Mix this with defog and permafrost, and Noctowl is suddenly a win condition that provides decent support. I haven’t tested this myself, since the battle simulator isn’t updated to the full release and I still need to train my delta Hoothoot, so most of this is just speculation.
Obviously this strategy has counters; you can’t just throw it out turn one and instantly win. A 130 base speed pokemon with max speed investment will have exactly 1 more speed than a choice scarfed Noctowl, and any pokemon running a priority move will be able to kill it through its measly 50 defense. Articuno’s typing is also really bad because of a quad weakness to stealth rocks, which limits Noctowl’s ability to revenge kill (so its not a Hoopa Unbound again). However, after removing all threats, Noctowl can come in on a revenge kill and sweep the entire team. Even if just used as a stallbreaker, this power far outweighs any possible downsides.
There’s two versions I think are viable; scarf and sash. Scarf is obvious; come in off another pokemon fainting and either sweep the team for a victory or get a guaranteed revenge kill, and force them to switch to their scarf / priority move pokemon. The mere presence of Noctowl on a team can basically lockdown their sweeper, since losing it is an instant game over, which can support your other win conditions even more.
The second version I think might be a decent rouge pick is sash. This version is made to be a lead in; the idea is that you kill their lead before they can set up stealth rocks (or make that their only play), and then if you outsped them then you also get to kill the scarf user. Obviously its not as amazing, but the mere existence of this build can basically remove all sub 70 leads from the game, or force them to run sash themselves instead of leftovers (farewell Spider Metagross; I barely got to use you). Plus it makes leading against someone using a Noctowl even more risky if their normal lead is also their Noctowl counter.
I personally think that, if Insurgence had a competitive scene, Noctowl would either be one of the most meta defining pokemon in the game, or banned straight to AG right at the start. What do you think? Anything I missed, or that you would like to add?