OP is calculated by adding up the raw OP and then applying OP modifiers (mods).
Many races have a small amount of OP on their elite defensive units. For example, Human Knights have 2 OP and 6 DP. Although these units can be used as part of your OP, they are practically never used. When used, it's usually considered a suicide attack or a very small amount are sent when traditional OP units only barely do not break the target's DP.
A suicide is an attack where the offensive power also consists of elite defenders, or when the attacker sends out an unsafe amount of offensive power leaving little turtle DP at home.
The amount of OP (modded, with bonuses) sent cannot exceed a ratio of 5:4 relative to DP (modded, with bonuses).
- Racial bonus: some races have a racial OP bonus; (Gnome and Troll).
- Magic: some races have a racial spell which gives an OP bonus; Human, Goblin, Nomad.
- Prestige: an important incentive for attackers, gained and lost through invading.
- Gryphon Nest: a modifier building often used later in the round, or early in the round as an aggressive push.
- Forges: a slower and efficient way to grow your OP with castle improvements.
- Morale: a multiplicative bonus which can lower OP bonuses.
All OP mods, except for morale, are additive (summed up together):
[Racial Bonus] + [Spell Bonus] + [Prestige Bonus] + [Gryphon Nest Bonus] + [Forges] = OP bonus
If morale is less than 100%:
( [Racial Bonus] + [Spell Bonus] + [Prestige Bonus] + [Gryphon Nest Bonus] + [Forges] ) * [Morale Penalty] = OP bonus
Temples are not considered an OP bonus and are not included in any OP calculations. Instead, it is considered a negative DP bonus for the target.