Titan7880
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Each race has different upgrade options. For Haven, you can take all new units (Rebels), except for Inquisitors. Sometimes, armor is more useful than Bloodlust.
For Academy, you can take all old units, except for Gremlins and Titans. For Necropolis, you can take all new units, except for Vampires. For Sylvan, you can take all new units, except for Druids and Archers. For Dungeon, you can take all new units (I especially like the new lizardmen).