How To Unlock All Summonable Units

For units unlocked by reaching a wave, you receive one in your current party whether or not you reached the summon limit. After your current session ends, you open their unlocked door in the UNITS tab in the Upgrade Shop.

Unit How to unlock
Dwarf Purchase unit for 20,000 Gold.
Engineer Purchase unit for 15,000 Gold.
Healer Unlocked by reaching Wave 4.
Necromancer Unlocked by reaching Wave 11.
Ninja Unlocked by reaching Wave 9.
Shaman Unlocked by reaching Wave 16.
Storm Knight Purchase unit for 30,000 Gold.
Tank Unlocked by reaching Wave 14.
Wizard Unlocked by reaching Wave 6.