Ok, this a question about megas, I'm not allowed to fail
(Mostly considering LGPE OU)
Mega Aerodactyl losing Tough Claws does not affect it much, as it has nearly unmatched speed and titanic attack.
Mega Beedril reacted similar to Aerodactyl, and it also has the strongest U-turn in the tier, be aware of its frailty and Stealth Rock weakness, though.
Mega Gyarados has an incredible typing for the tier and overall good stats, but be careful with Zapdos, Electrode, and Jolteon.
Mega Alakazam is a terrifying revenge killer, just be aware of the tier's dark types.
Mega Charizard X is one of the few dragons available, and it can do quite a lot of damage, plus it can viability run special sets thanks to it losing Tough Claws. Be careful with its Stealth Rock weakness.
Mega Gengar loss of Shadow Tag really hurts, but it's still one the best LGPE megas and still banned from OU.
Mega Charizard Y has an even worse Stealth Rock weakness than X, but it has a very good wallbreaking potential.
Despite Mega Venusaur losing Thick Fat, it still works well as a tank or even a mixed attacker.
Not that bad
Mega Slowbro's ability wasn't that useful to begin with, and it has titanic physical bulk, but Mega Gyarados and Starmie are overall better.
Mega Pinsir lost Aerilate, meaning it can't hit as hard now.
While Mega Blastoise isn't horrible, it losing Mega Launcher severely hurt it.
Mega Pidgeot lost No Guard, meaning there is no infinite accuracy Hurricane for it anymore.
Mega Kangaskhan lost its infamous Parental Bond, making it way, way worse.