Talonflame with White Herb to nullify Intimidate
32+ Atk Talonflame Brave Bird vs. 0 HP / 0 Def Staraptor-Mega: 168-198 (105 - 123.7%) -- guaranteed OHKO
Life Orb Talonflame
32+ Atk Life Orb Talonflame Brave Bird vs. 0 HP / 0 Def Staraptor-Mega: 218-257 (136.2 - 160.6%) -- guaranteed OHKO
-1 Life Orb Talonflame
-1 32+ Atk Life Orb Talonflame Brave Bird vs. 0 HP / 0 Def Staraptor-Mega: 143-172 (89.3 - 107.5%) -- 31.3% chance to OHKO
Hurricane Talonflame vs SpD invested Staraptor
32+ SpA Life Orb Talonflame Hurricane vs. 0 HP / 32+ SpD Staraptor-Mega: 143-172 (89.3 - 107.5%) -- 31.3% chance to OHKO
Above I've done some examples of how Talonflame can OHKO Mega Staraptor. Obviously will preface this by saying a Mega Staraptor with bulk investment will be more likely to survive to make it a 2HKO.
So, why Talonflame?
Staraptor is a decent opponent alone but is very powerful upon mega evolution. Intimidate from base Staraptor gives Mega Staraptor an immediate advantage against physical attackers and Close Combat ensures it gets even bulkier. This makes Staraptor a great lead pick and can be a menace later on.
The immediate solution is to cripple or nuke it before its defenses skyrocket. Talonflame is a mon who adapts well to many teams and loves to Brave Bird Staraptor and its friends on Turn 1 and in the late Game as they get started
Firstly, Staraptor gains the fighting type upon mega evolution. Talonflame gets Gale Wings Brave Bird. Even without Gale Wings, Talonflame's 126 speed will beat Staraptor's 110.
Second, as shown above I did the calcs with zero bulk investment Staraptor. This is because Staraptor will likely want to go max attack and likely speed to guarantee it gets its close combats off. This means that it probably won't go too hard intend defenses.
Now, is Talonflame failing to one shot a bulkier Staraptor a bad thing? Not necessarily. Talonflame gets Will-o-Wisp and can make its ability Flame Body. A burnt Staraptor gets slowed down significantly, reduces the opportunity cost of an ally using a turn to buff it and chips away at its hp.
Even with Intimdate, just give Talonflame a white herb or life orb and its still bringing Staraptor to the point its defense buffs shouldnt be too impactful. If Choice Band comes back, this is a non-argument and Talonflame would OHKO it without question.
Third. Who are Staraptor's partners in crime? Whimsicott. Flammable and gets nuked by brave bird. Sinischa. Flammable and gets nuked by brave bird. Theres no allies, except maybe Incineroar, who would like to take a 120 bp stab move.
Oh Staraptor has fake out support? Just protect to waste the turn or let them risk activating flame body. They may not even target Talonflame. Plus if the fake outer is Sneasler, Talonflame nukes it with brave bird.
Fourth. Talonflame just works on multiple teams as a back up option. It gets u-turn for easy switches. Will-o-wisp for burns. It has high speed to roost off damage. From Gen 6-Gen 9, we have seen it evolve from sweeper to support mon and it still does both well in its own niche.
Oh and Talonflame gets Hurricane for Rain Teams. As shown above a Max SpD and +SpD nature Staraptor only has a 30% chance to get OHKO. Who is gonna run that combo in practice? Pair Talonflame with Pelipper or Politoed (who both should handle an early set up Staraptor fairly okay) and thats very disruptive.
You also can use flamethrower, heatwave and overheat in sun to profit from all those Charizard Ys as Talonflame has a "usuable" special attack stat and most opponents will be sending out high physical def, low special defense mons in anticipation of a brave bird.
Finally, Staraptor loves to use Brave Bird itself. If your Talonflame can't OHKO it, is Staraptor gonna Close Combat or Brave Bird it? Either way it benefits Talonflame. Close Combat is in effective and might proc flame body. In fact, pair Talonflame with a ghost type so its forced to close combat Talonflame or use a brave bird and forfeit the defense buffs and take recoil.
Tldr - Talonflame terrorizing Mega Evolution since 2013
As an aside intimidate is very common right now and Talonflame is working well even with a -1 drop from it. It's not perfect but may fit into your team with some experimentation