Every creature has one or more effects.  They are listed as follows:

General Effects:

Name Effect
Resist Ignores enemy element if enemy's power is lower than number

On Win Effects:

Name Effect
Bandage Recovers health and removes Bleeding
Bleeding Deals damage to your opponent for a number of rounds
Damage Deals bonus damage to enemy
Drain Steals health
Elemental On an Elemental Win deals bonus damage
Explode Deals damage to your self
Pierce Ignores enemy armour under a certain amount
Poison Deals Poison damage over a number of rounds
Sap Recovers a percentage of damage dealt
Weaken Reduces enemy power for next round by a %

On Loss Effects:

Name Effect
Lifetap Deals damage to your self
Noxious Deals Poison Damage over number of rounds to the enemy 
Revenge Deals damage to the enemy
Shield Reduces damage taken