Pure Strategy is a game mode similar to Survival. The Eternia Crystal and defenses must last through an extended number of waves on a given map, with progressively harder enemies. However, there are several key differences:
- During the combat phase, players can only move their hero, upgrade defenses and pickup items.
- The ability to build new defenses, sell or repair defenses, use hero skills, attacks or abilities, or having a familiar attack enemies is disabled. (Passive familiars such as Guardians will continue to boost defenses in combat.)
- Enemies do not have any elemental resistances.
- Enemies do not target and cannot damage heroes.
- Heroes pass through towers and enemies instead of colliding with them.
- Special DLC Nightmare monsters (Djinn and Sharken) do not spawn on all maps. Spiders still spawn, but in far fewer numbers.
- Ogres will not spawn, despite the "Ogre Has Arrived" notification.
The rewards of Pure Strategy mode are identical to those of Survival (see Survival Rewards).
Because repairs are not allowed during the combat phase, upgrades become the only way to restore a tower's health during the combat phase. The party must balance between the effectiveness of their defenses and the number of times they can be upgraded. In preparation for longer waves, it may become necessary for the party to replace upgraded defenses with non-upgraded ones to ensure that they last the entire wave. Monk auras and Huntress traps generally expire relatively quickly, and are often the first to be replaced.
Equipping Guardian familiars will make things much easier since they still boost defenses in combat.