Enchanted Realms Rulebook
Reactions
A combatant is permitted an action approximately every 10 counts of the tracker; however, there is another opportunity for that entity to have further impact on the combat. This is through a game mechanic called a reaction. A reaction is an instant response to a trigger of some sort. This trigger can occur on the player’s turn or due to action of someone or something else. In terms of timing, unless stated differently in the description, the reaction happens immediately after the trigger condition occurs. Should the reaction interrupt another creature's turn, then that creature can continue its turn right after the reaction is processed.
However, once using a reaction, there is a cool-down period before another reaction can be used. That value is a static count of 8 with no modifiers. It will not be noted in the Roll20 tracker. Instead, the flex marker 
will be displayed on the character’s token, which will disappear 8 counts later.
Some reactions are basic ones which anyone can perform, while others require a skill (or possibly a magic spell) to be able to use. Reactions are not required to use, but they are limited to one use per creature per combat round. Just like actions, the reaction counter is reset at the start of the following round.
Examples:
• Dismount Unexpectedly: When a walking mount is incapacitated, the rider may use a reaction to land on his feet.
• Evade drive maneuver: A reaction can be used to avoid the effects of drive.
• Flee-attack: A melee combatant in an adjacent hex chooses to retreat from a stationary enemy, an attack as a reaction is permitted.
• Impalement: Reaction used against a charging opponent if using a reach weapon.
• Standing up: When knocked prone standing back up can be performed as a reaction to occur at the end of the the following initiative count. Otherwise, one’s stance is recovered at the next movement opportunity with no hex advancement. The timing of standing up may be penalized depending on the cause.