And Aegislash? If luke runs iron tail it gets walled by aegislash.
Here's the scary thing. If you have a SD off, most of the time Scenario plays like this
Player 2 sent Aegislash
Player 1 used swords dance
Player 2 King's Shield
Player 1 Swords dance
At this point here are the calcs
+2 252 Atk Adaptability Lucario Iron Tail vs. 252 HP / 0 Def (custom): 167-197 (51.54 - 60.8%) -- guaranteed 2HKO
So my opinion would be simply to find an Aegislash counter. Garchomp is a great one
Normal Luke = Extremespeed
Mega Luke = Bullet Punch
It depends on what your team needs. I understand LO Lucario ExSpeed are stronger but it's necessary to run on regular Lucario if Talonflames, Starmies, Scarf Keldeo are a problem.
The choice isn't that clear cut for Mega Lucario. They have exactly the same power, and Bullet Punch beats Mega Gengar while Extremespeed beats Talonflame, so it's a heavily team-dependent choice.
This individual has summed it up correctly.
Extremespeed can be useful to hit Choice Scarf Keldeo, Heatran and Volcarona. Anyway, +2 Bullet Punch is better because is boosted by Adaptability and OHKOes Gengar and Terrakion.
You could technically run both. BUT MegaLucario kills heatrands and Volcarona regardless. If Terrakion isnt scarfed, it looses to CloseC. If a gengar switches in onto you, you are faster EVEN if it megaevolves.
I've been having trouble with the pokemon that bullet punch can't cover, but I'm wary of giving up the method of dealing with Mega Gengar right now since my team doesn't have much in that department.
Serious question here, since I haven't used Lucario since gen IV: what should I be looking to switch into in order to get that SD off?
I've been playing around with it and I either force a switch, get the SD off and proceed to sweep or wildly mispredict and lose Lucario immediately.
You should post your team and we can see what to workout.
As for when, it really depends, whats why it's useful to have an encore on your team. For example,
4 Atk Tyranitar Crunch vs. 28 HP / 232+ Def Wobbuffet: 228-270 (43.18 - 51.13%) -- guaranteed 3HKO
After an Encore, this allows you to switch in and get a boost from Justified and a SD off.
Let's run calcs on that
+2 252 Atk Adaptability Lucario Iron Tail vs. 248 HP / 172 Def Landorus-T: 432-510 (113.38 - 133.85%) -- guaranteed OHKO
+3 252 Atk Adaptability Lucario Iron Tail vs. 252 HP / 36 Def Jellicent: 378-445 (93.56 - 110.14%) -- guaranteed OHKO after Stealth Rock
v+3 252 Atk Adaptability Lucario Iron Tail vs. 244 HP / 248+ Def Gliscor: 366-432 (103.97 - 122.72%) -- guaranteed OHKO
Again, posting your team would help
Small nitpick, but Adaptability Bullet Punch and Extremespeed have the same strength.
The difference between these moves is coverage; coverage is necessary because their power without a Life Orb is rather underwhelming. Bullet Punch allows you to pick on Scarf-Terrakion, Mega-Gengar with little effort but what utility does Extremespeed have? You have a solid answer to offensive Starmie who can outspeed and OHKO Lucario with Hydro Pump. It is not a good answer to Scarf-Keldeo, which takes quite a bit of grind-work in order to wear it down enough for Extremespeed to KO it and at this stage you probably will have figured its set out anyway. Lucario does not need coverage in order to KO offensive Volcarona (Choice-Volcarona is bonkers in Singles due the mere existence of Stealth Rocks) and there is no way you get past a Scarf-Heatran expect with something like Agility a Scarf on the regular one. Talonflame is a valid target but only the Adamant LO Brave Bird is enough to OHKO Lucario. If it has taken SR and one LO damage beforehand, it can be knocked down with Bullet Punch.
Just on the Talonflame note,
If Talonflame was adamant, then a CC would be the better choice as you outspeed Talonflame.
However, what I've been running into is Jolly Flying gem Tflame.
252 Atk Flying Gem (custom) Acrobatics (110 BP) vs. 4 HP / 0 Def Lucario: 219-258 (77.65 - 91.48%) -- guaranteed 2HKO after Stealth Rock
Sadly what this calc didnt take into account is the boost from Flying Gem