What does Head Smash hit exactly? If you want to hit Mega Altaria you might as well use Heavy Slam, which also OHKO's Diancie and doesn't give a lot of recoil. Though I think both Head Smash and Heavy Slam are rarely worth it considering Sucker Punch has the potential to be actually helpful in almost any match, whereas the coverage moves are matchup and prediction reliant. I prefer Life Orb over Choice Band because the ability to switch moves is so important when trying to wallbreaker bulky balanced teams. The extra recoil is a thing but at least you can go mixed and do much more damage to Lando-T / Garchomp with 4 SpA HP Ice which turns 3HKO's and a lot of recoil into 2HKO and only 20% recoil.
-1 252 Atk Life Orb Reckless Emboar Flare Blitz vs. 252 HP / 240+ Def Landorus-T: 153-181 (40 - 47.3%) -- 43.8% chance to 2HKO after Stealth Rock
-> 1 / 3 + 1 / 5 + 31% recoil from Life Orb, Flare Blitz and Rocky Helmet, not guaranteed 2HKO
-> Leftovers helps with the less recoil damage but requires an extra LO hit and Stealth Rocks for Lando-T
252 Atk Life Orb Emboar Superpower vs. 240 HP / 176+ Def Garchomp: 196-231 (47 - 55.3%) -- guaranteed 2HKO after Stealth Rock
-> Not a 2HKO because of Superpower power drops. Total recoil after 2 Superpowers is 78%. Garchomp will probably outspeed because it often goes high enough for Bisharp and if it doesn't attack you right attack but use Stealth Rock, it will take those 2 Superpowers and have somewhere around 1% and 21% left so you will still lose 1v1 and Garchomp got its rocks up.
So those are two really bad scenario's that can easily become:
4 SpA Life Orb Emboar Hidden Power Ice vs. 252 HP / 8 SpD Landorus-T: 270-322 (70.6 - 84.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
4 SpA Life Orb Emboar Hidden Power Ice vs. 240 HP / 0 SpD Garchomp: 260-307 (62.3 - 73.6%) -- guaranteed 2HKO after Stealth Rock
If you're going for mixed and you see Grass Knot in the teambuilder and you think it's a good idea: don't use it. Its two main targets (Hippowdon and Slowbro) are already 2HKO'd by respectively Flare Blitz and Wild Charge. No recoil is a pro of Grass Knot ofcourse but it doesn't weigh up to losing Wild Charge, because it disables you to OHKO Starmie, Manaphy and Talonflame.
-1 252 Atk Life Orb Reckless Emboar Flare Blitz vs. 252 HP / 240+ Def Landorus-T: 153-181 (40 - 47.3%) -- 43.8% chance to 2HKO after Stealth Rock
-> 1 / 3 + 1 / 5 + 31% recoil from Life Orb, Flare Blitz and Rocky Helmet, not guaranteed 2HKO
-> Leftovers helps with the less recoil damage but requires an extra LO hit and Stealth Rocks for Lando-T
252 Atk Life Orb Emboar Superpower vs. 240 HP / 176+ Def Garchomp: 196-231 (47 - 55.3%) -- guaranteed 2HKO after Stealth Rock
-> Not a 2HKO because of Superpower power drops. Total recoil after 2 Superpowers is 78%. Garchomp will probably outspeed because it often goes high enough for Bisharp and if it doesn't attack you right attack but use Stealth Rock, it will take those 2 Superpowers and have somewhere around 1% and 21% left so you will still lose 1v1 and Garchomp got its rocks up.
So those are two really bad scenario's that can easily become:
4 SpA Life Orb Emboar Hidden Power Ice vs. 252 HP / 8 SpD Landorus-T: 270-322 (70.6 - 84.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
4 SpA Life Orb Emboar Hidden Power Ice vs. 240 HP / 0 SpD Garchomp: 260-307 (62.3 - 73.6%) -- guaranteed 2HKO after Stealth Rock
If you're going for mixed and you see Grass Knot in the teambuilder and you think it's a good idea: don't use it. Its two main targets (Hippowdon and Slowbro) are already 2HKO'd by respectively Flare Blitz and Wild Charge. No recoil is a pro of Grass Knot ofcourse but it doesn't weigh up to losing Wild Charge, because it disables you to OHKO Starmie, Manaphy and Talonflame.