Guild Wars 2

Time attack
Explorable mode, but with a twist. In time attack, the final reward is dependant on clear time rather than set to a specific number. Higher rewards for those who’re quick, however dally too much and the reward will be less than regular mode. This is for all those who wish to speedrun or challenge themselves to a personal best.

Possibly, this could be a Guild Unlock and the High Scores would be kept within the guild to promote friendly competition and bragging rights. (Friendly competition in an MMO, pfff… who am I kidding?)

Gauntlet
Essentially a “Hard mode”, Gauntlet would give all enemies in the dungeon Invulnerability at set intervals for a specific amount of time (Numbers subject to change, of course):

*Trash mobs: 1s Invulnerability every 15s
*Veterans: 1s Invulnerability every 10s
*Elites: 2s Invulnerability every 12s
*Champions: 3s Invulnerability every 15s + Quickness for the duration.
*Bosses/Legendary: 6s Invulnerability every 18s + Quickness for the duration.

This would force players to rethink the tried and trusted “Stacking” techniques because of the simple fact that they’d merely be sitting ducks while it happens. That’s not to say that can’t stack, but mobility and right choice of utility skills would suddenly take a lot more priority than regular runs. Of course, the reward for clearing a dungeon run like this would obviously be substantial, to accomodate for the increased difficulty.

Survival
No Waypoints. Constant Maximum Health debuff (I.e the red arrow on your health bar that says “you go down, you’re defeated”). Oh, and enemies all are Frenzied (I.e deals more damage with a buff that can’t be removed or stolen). Best of luck.

I am not so sure I like your first idea.
I think there is enough focus on time already, hence the constant: LF zerg warriors only!
Many classes would be in a disadvantage with this.

I would rather see something that made more professions and more versatile builds desired in dungeons.