There are a total of 8 Boons in Guild Wars 2, each causing a positive effect on the recipient. Boons tend to be considered the polar opposite of Conditions with each Boon causing an effect for a limited duration. Boons stack in Duration but with the exception of Might, their effectiveness does not stack. You could not for example have two stacks of Protection (which would give 66% damage reduction) instead, you are limited to just one Protection Boon (33% damage reduction). Boons are designed to support any number of play styles as well as offer significant improvements to your character even if it is only for a short period.
Almost all professions have access to several boons though some, like the Guardian, excel at creating or distributing guild wars 2 gold. Boons only tend to last several seconds due to their potency but this is often enough to provide you or allies with a significant buff.Unlike Conditions, many Boons (with the exception of Regeneration and Retaliation) function at their maximum potential without the necessity to invest in any attributes. However, Boons can still be stripped by other players, meaning Boon heavy builds (where a player relies on their continued benefits) can be left vulnerable should they come across an individual intent on removing them.
Aegis – Block the next attack.
Aegis is a Boon that for all intents and purposes is unique to the Guardian. Although the Mesmer can obtain it, this would be based purely on random acquisition rather than a guarantee (from Chaos Storm and Signet of Inspiration). The Guardian however can regularly obtain it through the use of their Virtues (Virtue of Courage) as well as a multitude of traits and a single skill (Retreat!). Aegis guarantees that the next attack on you is blocked (similar in functionality to Blind) making it incredibly powerful in mitigating damage and makes Guardians, who focus on its use, very difficult to damage if its use is timed right.
Fury Fury – 20% Critical Chance increase. Stacks in duration.
Fury provides a flat 20% improvement to your critical strike chance, allowing for some wriggle room in terms of your character setup. For example, if you know your profession can guarantee Fury in certain situations and you seek to crit regularly (50% would be more than sufficient) you could aim for a base of 30% in the knowledge that when a fight does break out, you can drink (in the Engineers case) an Elixir B to gain an instant 20% boost, taking your total amount to 50%. Alternatively, as there is no cap to your chances of landing a critical hit there is the potential to achieve a significantly higher value. In most circumstances, this Boon really has no negatives and will, irrespective of setup, provide you with a brief benefit to your damage.