Mega Druddigon
Typing: Dragon ----> Dragon/Steel
Abilities: Rough Skin/Sheer Force/Mold Breaker ----> Photovoltaic (Chlorophyll clone)
BST: 77/120/90/60/90/48 ----> 77/135/135/60/110/68
New Moves: Bulk Up, Iron Head, Wild Charge
By reworking the wings into solar panels, Mega Druddigon become some sort of syborg-gargoyle-thingy. Dragon/Steel is an awesome defensive typing, being neutral to Fairy, Dragon and Fire, Dragon and Steel types' respective weaknesses, and is only weak to Fighting and Ground, both of which have mostly physical users, thus Mega Druddigon's higher Def. Photovoltaic allows it to have a decent speed while still maintaining bulk, and 135 Atk isn't bad either, letting it use Bulk Up to buff up its Atk and Def. However, outside sunlight Mega Druddigon has a medicore speed, and can be easily outsped.
Mega Golurk
Typing: Ground/Ghost ----> Ground/Ghost
Abilities: Iron Fist/Klutz/No Guard ----> Grounded (All immunities to Ground are ignored when user is on the field.)
BST: 89/124/80/55/80/55 ----> 89/159/130/55/105/45
New Moves: Shadow Claw, Automize
This one is designed as a Spinblocker that can also scare out Defoggers. Grounded makes it so Flying types, Levitate, Air Balloon etc. lose their immunity to Ground, and considering most of the Defoggers are either Flying type or have Levitate, this is a huge boon against them. Skarmory can't really switch in, as it will swiftly be 2HKOed; Mega Charizard Y gets OHKOed instead. Most other Defoggers fare the same, with only Mandibuzz able to escape the 2HKOes. it also has a much better bulk, able to live a CB Dragonite's Outrage with only full investment in HP. While its Speed is lowered slightly, it also has Automize to boost its speed and can attempt to sweep.
Mega Bisharp
Typing: Dark/Steel ----> Dark/Steel
Abilities: Defiant/Inner Focus/Pressure ----> Swordsmaster (Boosts Blade, Cut, Slash, and Sword moves by 1.5x)
BST: 65/125/100/60/70/70 ----> 65/170/85/80/60/120
New Moves: Sacred Sword, Leaf Blade
Bisharp looks sooo much like a
Kamen Rider it can't be more obvious. Especially
Kamen Rider Accel. So, I kind of based Mega Bisharp on Accel's Trial form, in which it loses armor in favor of more speed. Mega Bisharp now is much faster than before, able to outspeed many opponents without using Sucker Punch, and its Atk is buffed straight up to 170, which is among the higher ones of the megas. With the addition of Sacred Sword and Leaf Blade, it has most of the move boosted by Swordsmaster, and with its speed and high Atk, it can make good use of them. However, Mega Bisharp's bulk becomes downright medicore in return, which makes it easy to faint. It loses at least 70% HP to CB Ledian's Mach Punch.
LEDIAN. Basically, any Mach Punch users can ruin it easily. Special attackers can also target Mega Bisharp's even frailer special side.
EDIT: The problem with giving Mega Mienshao Scarecrow is that there's no way it fits flavor wise. Though I support GG unit's suggestion:
Or maybe have Scarecrow also deliver recoil damage to contact Flying-type attacks? That would make sense in that something using Brave Bird wouldn't actually be missing, but rather hitting the scarecrow instead. Guts is better than Toxic Boost too.