Mana
Overview
In Dungeon Defenders II, each hero has two separate mana pools; Blue, and Green. Blue mana is used to activate Hero Abilities and Green mana is used to Build, Repair and Upgrade defenses.
This system is based off of Dungeon Defenders, where there was only one type of mana, and that mana would be used to both activate abilities and build towers.
Blue Mana
Blue mana (also known as "Ability Mana") is used to activate hero abilities. It regenerates passively during the Combat Phase, albeit slowly. It also completely regenerates at the start of each new combat phase. Since mana doesn't disappear between rounds, you can drop all of your mana and have effectively twice the blue mana to spend in a round. The values for blue mana's regeneration rate are currently unstudied. Blue mana does not increase per level and is set to 250.
Green Mana
Green Mana (also known as "Building Mana") is used to Build/Repair/Upgrade defenses. It is obtained exclusively from defeated Enemies and Mana Nodes. Unlike Blue Mana, Green Mana does not regenerate and does not refill at the start of a combat phase. It does however increase its maximum capacity as a hero Levels Up.