Activation - When a debuff tries to take effect on the target.
Application - When a debuff successfully applies or "lands" on the target.
Resistance - the target's chance to prevent application of a harmful effect.
Accuracy - the attacker's ability to bypass resistance.
Rate of Resistance - The actual chance that an effect is resisted, which can be found by subtracting Accuracy from Resistance. The Rate of Resistance cannot go below 15%.
Beneficial Status Effect (Buff) - Any effect that can be applied to allies to increase their effectiveness in battle. Examples include Increase Attack Power, Increase Critical Rate, Immunity, etc.
Harmful Status Effect (Debuff) - Any effect that can be applied to an opponent to reduce their effectiveness in battle. Examples include Attack Power Reduction, Defense Reduction, Stun, Freeze, Attack Bar Reduction, etc.
Skills - The actions which can be performed by a monster in the game. Skills include attacking 1 or more enemies, applying buffs to your own monsters, applying debuffs to enemies, healing, etc. Some skills include multiple effects, such as attacking and debuffing, healing and buffing, etc.
Any skill which inflicts a Debuff or a negative effect of any kind on an enemy monster will normally have an activation rate going up to 100% (this will usually be noted in the skill description). However, an entirely separate mechanic also exists which determines whether a debuff or negative effect actually ends up applying on a monster. This is the mechanic of Accuracy and Resistance.
All monsters possess a certain amount of Resistance ranging from a base of 15% up to 100%. Resistance simply determines the likelihood of any negative effect actually applying. The higher the resistance, the lower the odds of successfully applying a negative effect. Resistance works entirely separate from the activation rate of a skill.
It may be easiest to think of this as a series of dice rolls or "checks". The first dice roll or check determines the odds that any given negative effect will end up activating, and a second dice roll or check will determine whether the effect will apply on a monster. Both events are independent of one another, with neither influencing the outcome of the other directly, although if the first dice roll fails, the second will not take place at all.
Accuracy acts as a function of resistance, and simply represents the odds of bypassing resistance. The higher the accuracy, the greater the likelihood that resistance will not come into play (and the greater the odds of successfully applying an effect).
To determine the exact odds that an effect will be resisted, one need only use the following formula:
For example, if a monster has accuracy of 45% and tries to apply an effect on a monster with resistance of 90%, the final resistance chance will be 45% (meaning that there will be a 45% chance of an effect being resisted).
One important caveat to this formula is that the Rate of Resistance cannot go below 15% (the base resistance of all monsters). In effect, this means that should accuracy surpass resistance, there will still always be a base resistance rate of 15%.
The Light Inugami's Scratch skill has the following effect: Attacks with giant claws to decrease the enemy's defense for 2 turns. Since the activation rate is not mentioned, one can reasonably assume that the activation rate for this effect is 100% (meaning a guaranteed rate of activation). Let's also assume for this example that this particular monster also has 60% accuracy. Now let's say it attempts to apply this effect on a Water Epikion Priest with 85% resistance.
In this example there will be two dice rolls or checks, one for the activation of the defense debuff, and one for the Rate of Resistance for Water Epikion herself. Since the first check is guaranteed to activate the debuff, we can move on to the second check, which is the Rate of Resistance itself. Since Epikion's resistance is 85%, one need only subtract Inugami's 60% accuracy to determine the final resistance rate.
Thus, there will be a 25% chance that Inugami's effect will be resisted and consequently fail to apply.
The Light Inugami's Scratch skill has the following effect: Attacks with giant claws to decrease the enemy's defense for 2 turns. Since the activation rate is not mentioned, one can reasonably assume that the activation rate for this effect is 100% (meaning a guaranteed rate of activation). Let's also assume for this example that this particular monster also has 60% accuracy. Now let's say it attempts to apply this effect on a Water Epikion Priest with 45% resistance. To determine the resistance rate, we simply subtract Inugami's 60% from Epikion's 45%.
It should be noted that numbers normally cannot be less than zero in Summoners War, so the resistance rate in this case will end up processing as 0%. But as mentioned previously, the Rate of Resistance cannot go below 15%. Thus, there will be a 15% chance that Inugami's effect will be resisted and consequently fail to apply.
The Wind Inugami's Scratch skill has the following effect: Attacks the enemy with razor-sharp claws and decreases their defense for 2 turns with a 50% chance. This means there is a 50% chance that this effect will successfully activate. Let's also assume for this example that this particular monster also has 60% accuracy. Now let's say it attempts to apply this effect on a Water Epikion Priest with 85% resistance. To determine the resistance rate, we simply subtract Inugami's 60% from Epikion's 85%.
Thus, the final Rate of Resistance will be 25%, meaning that there will be a 25% chance that Inugami's effect will be resisted and consequently fail to apply.
However, note that Wind Inugami's activation rate for Scratch is only 50%. To determine the actual chance that the effect will apply, we need to consider two dice rolls or events: the chance that Scratch will activate, and the chance that Scratch is resisted. This can be done with some basic probability math. For this example, it is assumed that you have no background or knowledge in probability.
To find the odds that Scratch will apply in the end, we simply need to multiply the odds of success in event 1 with the odds of success in event 2. In this case, Scratch has a 50% chance of succeeding, so event 1 will be 50%. For event 2, the odds of Scratch not getting resisted is 75% (the Application Rate, which is the opposite of the Rate of Resistance), so event 2 will be 75%. Now we just need to perform the calculations like so:
Thus, the final odds of Scratch being successful is 37.5%.
If the attack is a glancing hit, then, with few exceptions, activation is prevented and the process stops right here.
Though Glancing hits do not affect the Rate of Resistance or the Application of a skill directly, they do affect the activation of a skill. With the exception of skills that remove buffs, and harmful effects from passive skills, a Glancing Hit will prevent Activation.
Multiple debuffs from same skill
Some skills can apply more than one debuff, and it should be noted that each debuff will be run through this process individually. Just because one debuff activates and applies does not mean that all will. Some skills hit multiple times and, depending on the mechanics of the specific skill, each hit may have a chance to activate and apply a debuff.
Skills that Ignore Resistance
Some skills skip the resistance check and apply every time they activate. This is usually noted in the skill description (as in the case of Tiana), although ambiguous wording can imply guaranteed application despite this not being the case (e.g. Burentau and Lindermen). In some cases, a skill may not mention this at all (e.g. Elucia). For a more comprehensive list, use the Monster Filter to search for the support category Ignore Resistance.
Note that even a skill which ignores resistance can still fail to activate if the attack was a glancing hit; or the harmful effect can still be prevented by the immunity buff or passive immunity.