Cover

To Cover
In Guild Wars, covering means to stack certain things (Conditions, Enchantments, Hexes) so that when they are removed, the more important one remains while the less imporant one, or "Cover" is removed. Covers are usually easily reapplied because of their cheap costs and/or fast casting times.

Common Condition Covers:
Apply Poison + Crippling Shot; The Poisoned condition covers the Crippled condition, which is the desired condition.

Blinding Flash + Enervating Charge; The Weakness condition covers the Blind condition, which is the desired condition.

Eviscerate + Axe Rake; The Crippled condition covers the Deep Wound condition, both are desired, but deep wound is more hazardous to the enemy and required for Axe Rake to have an effect.

Common Hex Covers:
Parasitic Bond; Covers most necromancer hex spells. The cheap cost (5 Energy) and quick recharge make this ideal for a cover hex.

Conjure Phantasm; This hex is fairly powerful by itself, but covering important hexes like Migraine or Fragility, this can be equally valuable.

Wastrel's Worry; This hex is very cheap and very Spammable. This is usually used to encourage casting while covering Backfire, Soul Leech, or Spiteful Spirit.

Mind Wrack; This hex is cheap, fast casting, fast recharging, and long duration, making it an ideal Mesmer hex cover. It synergizes well with energy draining skills.