Mega Crustle
Type: Same
Ability: Sturdy/Shell Armor/Weak Armor --> Water Absorb
Stats: 70/95/125/65/75/45 --> 70/125/155/65/100/45
Mega Crustle is quite a nice wall. It only has 2 weaknesses, Rock and Steel. One of these is unfortunately quite common, but the other is really not seen much outside of Scizor. It can switch into Water type moves in order to heal itself, which is really nice espically when considering how common it is. Mega Crustle can also serve as a Shell Smasher, with plenty of attacking powers and a immunity to scald.
Mega Scrafty
Type: Same
Ability: Shed Skin/Moxie/Intimidate --> Shed Skin
Stats: 65/90/115/45/115/58 --> 65/120/125/45/125/108
New Moves: Coil
Mega Scrafty is now a powerful set up sweeper. It can use Coil to get perfectly accurate High Jump Kick and if it boosts high enough, Head Smash goes under the same situation. Its got a moderate amount of bulk on both sides and its new speed lets it outspeed a certain amount of threats. It can also run a double dance set that will also let it get its speed up. Shed Skin lets Mega Scrafty gets rid of some of those nasty burns and it also makes a lot of sense flavour wise.
Mega Sigilyph
Typing: Same
Ability: Wonder Skin/Magic Guard/Tinted Lens --> Wonder Skin
Stats: 72/58/80/103/80/97 --> 72/68/100/143/100/107
Mega Sigilyph is a powerful user of the move Stored Power. It is immune to Hazards other than Stealth Rock and it is immune to Earthquake. Its wonder skin helps it out by not making it completely immune to Taunt and Whirlwind, but it does make them rather inaccurate against Sigilpyh. It also gets some nice STAB to hit dark types with who are immune to Stored Power.
Mega Cofagrigus
Type: Ghost --> Ghost/Steel
Ability: Mummy --> Mummy
Stats: 58/50/145/95/105/30 --> 58/80/155/110/125/40
New Moves: Flash Cannon
Mega Cofagrigus is pretty much a improved form of its base form. It gets a good amount of special bulk so it can be usable on special attacking/walling sets and its new type gives it a immunity to toxic. It is weak to some common attacking types, but its typing is overall pretty good, as you can see with Aegislash, a poke who shares Mega Cofagrigus' typing. It keeps its ability since its a rather good one and there is no reason to change it.
Diamond Storm is also a welcome upgrade to Stone Miss... but if people are butthurt over signature move status, then pretend it's not there and vote regardless.
Please don't say stuff like this, its rude, thoughtless, and just makes people want to vote for it even less. Not likeing a submission just because it contains a signature move, especially a legendary signature move, is perfectly reasonable (Although I only do the latter.) when it comes to flavour.