Of all the wizarding guilds in Earthland, none are stronger or more infamous than Fairy Tail. This group of evil-fighting heroes is just as famous for their combat prowess as they are for racking up massive amounts of property damage, and a not insignificant part of those property damage bills come from Gildarts Clive, one of Fairy Tail's strongest mages. The middle-aged, often-absent Gildarts practices a form of magic which is so powerful that he could easily destroy his town if he happened to slip (which has happened before).
Note on canon:
Multiple times in the end-of-volume Q&As, there are indications that anime-only content is canon to the manga story, such as here and here. Thus, this RT will include anime-only content.
In the Tenrou Island arc, there is a tree on the island which increases the power of Fairy Tail guild members on the island (until it's temporarily negated); Feats taking place on this island while the tree is still standing will be marked [Tree].
After the Tenrou Island arc, there is a seven year timeskip. During those seven years, they were magically kept in suspended animation by a magical power, not aging a day. By author statement, the affected characters were no stronger afterwards than they were before the timeskip. Therefore, those feats are not marked separately.
After the Tartaros arc, there is another, one year timeskip. Feats from after this timeskip will be marked [PT]
Crush Magic
Gildarts's magic is to crush he touches into dust - or more accurately, to break what it's used on into pieces
Versatility
[Tree] Breaks the ground underneath him to absorb the impact from a punch
[Tree] Splits Natsu into several, smaller Natsus, then reforms them into one
Strength
Destroys several magic blasts, punching a guild wizard through a giant cube
[Tree] Sends Bluenote flying
[Tree] Destroys the ground underneath him, then creates a massive crater by clashing with Bluenote
[Tree] Blasts Natsu away
[Tree] Destroys Bluenote's "black hole" magic
Physicals
Strength
Punches the Cardinal into the ceiling, creating a shockwave from the force
[Tree] Blocks Natsu's punch
[Tree] Withstands a "black hole" magic that sucks in enemies
[Tree] Punches Bluenote so high into the air the force breaks the cloud cover over the island
Agility
Durability
Reputation