Solrock-Mega
Ability: Levitate ----> Desolate Land
Typing: Rock/Fire
Stats:
HP: 70
Attack: 95 ----> 145(+50)
Defense: 85 ----> 125(+40)
Special Attack: 55 ----> 35 (-20)
Special Defense: 65 ---->105(+40)
Speed: 70 ----> 60 (-10)
Base Stat Total: 440 ----> 540
Movepool Additions: Sacred Fire, Morning Sun (as Level-up)
Flavor Description: Solrock is now Fire-type, as should it kind of should have been in the first place. Its sunbeams are now white-hot plasma - the lower ones are even dripping a bit. The main body is now smoother. Its eyes are now wide open. Sacred Fire is not only obvious STAB, but the sun is considered sacred in many cultures - including in Japan, and you know where Pokemon comes from...
Competitive Description: Bulky physical attacker. While it has many similar properties to Primal Groudon, its many flaws (you know, the thing Primal Groudon doesn't have) stop it from turning the metagame on its head - but it's still a force to be reckoned with! Notably, a prime force in the metagame - Keldeo - can switch in no problem - as can Infernape. Garchomp and Swampert can also switch in well as long as they don't get burned. There's plenty other things that can switch in with a little bit of prediction, which shouldn't be too hard. It won't end weather teams - It still has a huge Ground weakness for Swampert, Garchomp, Hippodown, and Excadrill to exploit, after all.
Lunatone-Mega
Ability: Levitate ----> Eclipse (similar to Desolate Land, with a typing difference: It increases the power of Fairy attacks, and negates Steel attacks.)
Typing: Rock/Fairy
Stats:
HP: 70
Attack: 55 ----> 35 (-20)
Defense: 65 ----> 125 (+60)
Special Attack: 95 ----> 115(+20)
Special Defense: 85 ----> 135(+50)
Speed: 70 ----> 60 (-10)
Base Stat Total: 440 ----> 540
Movepool Additions: Surf, Power Gem, Moonlight (as Level-up)
Flavor Description: Look ma, new ability! The moon in Pokemon has always been associated with fairies, so making Lunatone fairy-type made sense. Power Gem is a better special STAB. Surf is mostly just because the moon influences the tides, but it's still a good. Moonlight is duh.
Competitive Description: Boy, Rock/Fairy would be a great type if it wasn't 4x weak to Steel... might as well make Lunatone immune to its main weakness! Its stats are nothing exceptional, but they're good enough to support Mega Lunatone's great combination of typing, ability, and moves. So I've gone over what makes it good, but it still has weaknesses. For something that gives out a sun variant, it's awfully weak to Grass. Its ability also doesn't patch up the fact that Steel-types still wall it. Hail is the only weather I can think of that doesn't have a counter to Mega Lunatone - Rain has the countless water-types, Sand has a lot of checks and oh Excadrill wrecks, and Sun has LITERALLY ANYTHING THAT CARRIES SOLAR BEAM, so it shouldn't be an end to weather teams.