Courageous Dimachaerus

These units are the special units from the Coliseum event that you can get to join your army. While slow, their high armor makes them difficult to bring down (and unusually for a regular unit, they have both armor and evasion values), and they are capable of doing staggering amounts of damage when they close. Their attack (although it's hard to say for certain) also appears to have some area of effect, as it can reduce multiple enemy units to ash simultaneously.