Creative use of game mechanics

Cancel logout macro allowing you to reach stupid heights of exploration.

Creative use of game mechanics was a term used to describe exploits that were usually in the grey area of being usable or a bannable offense.
For the most part these were mechanics that didn't have too much of a direct impact to most players. If it impacted the economy heavily, or let someone solo a current tier final boss then it would be considered a game breaking bug. Generally these days the only real clever use of game mechanics are raid/dungeon/m+ based to force an upper hand on a boss and it's blizzards job to patch a fix as soon as they can. There were a large array of these in dungeons which people used heavily for increasing their speed throughout M+.

Severe Exploits

General

• Changing game files on the client so that WSG doors or BWL doors were not visible on your client allowing you to walk right through. Also commonly used to make it look like you were wearing gear you weren't or changing your character model. Ranoki played around a lot with remodeling his character before patch 7.3 finally disabled the ability to do so.

Vanilla

• An exploit using a macro where you could jump logout and cancel logout which would let you float in the air and gain height resetting your jump. It allowed you to gain extreme height and was very quickly fixed.
  
• Breaking Bijou's for Zandalari reputation when your bags were too full to receive the token it created. This could be used to cap out reputation quickly. It can also be used to get your account banned forever if you're Popp.
• Cascading Raid Instances

Neat Tricks

General

• Mind Vision used just before a stealth class like rogue/druid would stay on them even while stealthed so you could just Shadow Word: Pain them out. Didn't get fixed until early MoP.
• There was a console script command which let you turn upwards until you were looking straight up, but instead of that being the limit, it let you continue going upside down.

Vanilla

• Out of combat resing in raid encounters during early vanilla before they forced boss encounters to make a zone wide combat flag.
• Eggsploits on the Razorgore encounter.
• Force Hearthing was a way to use a hearthstone when your one is already on cooldown. You would invite someone to a party while inside an instance, leave the group so the instance then becomes the new persons instance forcing you out after a 60 seconds timer. Back in Vanilla to Wrath hearthstones were a 60 minute cooldown making this strategy very useful to travel.
• With threat being as big of an issue as it was in Vanilla a trick Warriors could do to improve aoe threat was spamming Battle Shout and cancelling the aura. Every time the aura was applied it generated a fair amount of global threat. This could be made even stronger by putting a bunch of Hunters and Warlocks in the group with the Warrior so their pets were more targets for Battle Shout, making it even stronger.
• Disgusting Oozling pushing debuffs off. Mow used this to remove trick or treat debuff allowing him to steal all the candy from kids. Shadowalker used this trick to push the stomach acid debuff off during the C'thun encounter, making the fight significantly easier.
• The Shaman ability Sentry Totem caused the Shaman to freeze in place. This could be used as a safe fall when jumping down to Molten Core. Also you could drop it while running forward and it would appear that your character was running forward when it was not, tricking people into pulling a boss before it was go time.

Legion

• Rogues farming the Thunderfury skin bypassing the first 3 bosses in Neltharian's Lair by glidering across where the first boss is and then running on top of the entire instance and eventually jumping down at Dargrul.
• Rogues farming the Thunderfury skin bypassing to Ash'Golem in Vault of the Wardens by clipping through a wall and then gliding down on top of him.

M+ Strategies

Vault of the wardens

• The last boss of this instance required a light to show various things like unhide the boss which would come steal your light source and show the holes in the platform wide wall for the safe area's. There was a way to bring a second light into the fight which was intended. You could throw a light at a specific spot going down the stairs before you hit a trigger which would remove it, run past that trigger and pick it back up. This allowed you to have 2 lights for the boss speeding the kill up ever so slightly.