Enemies
Demon, summons portals using it's left hand to let enemies float through time.
Angel, locks up towers and forces you to buy them again. Kill them quick or your forces will be diminished...
Distractor, forces you to play a minigame occasionally. Don't fail, or else everything suddenly will become much faster than you remember...
Necromancer, revives dead allies at a fraction of their true power. Kill quickly or face the consequences of your past murders
Tyrant, taunts all towers in a certain radius and forces them to target him. Plan to slow him down as much as you can, or you may not be able to kill every enemy in time...
Allies
Ice Tower, slows down nearby enemies for 5 seconds
Fire Tower, sets nearby enemies on fire for 5 seconds
Rage tower, makes all towers stronger for a short period of time