I couldn't miss the chance to practice my drawing!
Every 30 minutes (real world time), a NPC called (camp name) battlewarden will appear on most Aetherytes and Aetherial gates, and up to fifteen players may join the behest. Five minutes after the NPC spawning, the behest will begin. If there are no players signed on that behest, the battlewarden will simply disappear.
Gameplay-wise, a Behest is much like a normal battlecraft Guildleve, even having the same usual 30 minutes timer. However, the difficulty level cannot be changed - with the monsters being around the same power as a 3 star monster on a battle leve - and there's no gimmick such as hidden creatures. Most behests also have some sort of Boss like monster at the end, being much stronger than the others.
The rewards for finishing a Behest are either gil or (very rarely) some sort of treasure. A player doesn't need to kill any monster to get the reward; just signing on for the Behest and staying until the end will make him eligible for the prize. Also, a player can forfeit and leave the behest group at any time speaking with the battlewarden again.
Behest has been discontinued in A Realm Reborn, replaced by Guildhests.