Blood thirsty and guard is also mentioned in The Official Mage Wars Rules Supplement on page 11 - Mandatory Actions. - COPY PASTE FOLLOWS
Some effects will require a creature to perform a specific action, such as making a melee attack against a
particular enemy creature in its zone. Currently, the only such effects are Bloodthirsty and Taunt. These effects
are referred to as mandatory actions.
A creature must perform a mandatory action if it is possible to do so when it chooses what action to perform. If
the creature is under multiple mandatory action requirements, the creature may choose which one of the
requirements to obey. These effects do not allow a creature to perform an action that would be otherwise
forbidden, such as attacking a creature that would otherwise be an illegal target (for example attacking a
creature when a different one is guarding, or attacking a Flying creature if the attacker is not flying).
Note that declaring the action includes paying any costs, so one would be required to pay any costs required to
perform the action. Determining whether or not the condition is possible is checked only at the moment that the
creature would be choosing its action (or target); the controller of the creature is not required to do anything
beforehand that would make the action possible. For example, the controller does not have to activate the ability
of another card (like using Archer’s Watchtower to give a ranged attack the Indirect trait) in order to make the
action possible.
Example: A creature with Bloodthirsty is in a zone with two other enemy creatures, one of which is Guarding
and undamaged, and the other one of which is damaged. Since the damaged creature is not a legal target for the
attack, the creature is free of any obligation to attack, so it could either attack the Guard or take another action.
Example: A creature with Bloodthirsty is in a zone with three enemy creatures, two of which are damaged, and
it uses a Sweeping attack action. The first attack must target one of the damaged creatures. For the second attack, it cannot target the creature it attacked in the first attack but it can still target the other damaged creature, so it must do so. If there were only one damaged creature and multiple undamaged creatures, then the first attack must target the damaged creature but the second attack could target any of the undamaged creatures.
Example: A creature is in the same zone as an enemy Sosruko which has Taunted him. When the creature
activates, since it is possible to attack Sosruko he must do so; he may not move out of the zone to avoid the
effect. Note that you could use your quickcast action to teleport the creature out of the zone before it activates,
so it wouldn’t be able to attack Sosruko and would not be bound by the Taunt effect.