Armageddon can cause even more damage to creatures than the Implosion if collateral damage is taken into account. Because Armageddon damages all creatures, it has become part of one of the most renowned tactics, often called Dragogeddon. The tactic requires fast creatures immune to Armageddon. In the original Restoration of Erathia, Gold Dragons and Black Dragons where the fastest creatures with immunity to Armageddon, and that is where the name of the tactic was probably derived. Later in Armageddon's Blade and Shadow of Death, the Phoenix became the fastest creature with immmunity to Armageddon. When the hero's army only consists of immune creatures, the hero may cast Armageddon without damaging his own creatures, in the process causing severe damage to the enemy.
The town with the highest amount of creatures immune to Armageddon is Conflux, with 4 out of 7 fully upgraded creatures being completely immune. On top of that, it's their highest-tier creatures. However, to balance that, Conflux cannot learn Armageddon at all in their Mage Guild.
The highest possible damage for Armageddon is 14,905 points per unit. This requires a level 108 hero with Expert Fire Magic, Expert Sorcery, Orb of Tempestuous Fire, maximum Power (99) and Sorcery as the hero's specialty (bonus 5% to Sorcery per level). The highest possible amount of unit stacks in battle is 20 per side + 3 War Machines per side. Therefore, the maximum possible damage to deal to all units on the battlefield, provided no spell immunity or resistance is in play, is 14,905 * 46 = 685,930 points of damage. However, if all creatures on the battlefield are Water Elementals, which are vulnerable to fire, highest possible damage is 14,905 * 2 * 40 + 14,905 * 6 = 1,281,830. However, because the maximum possible Power is 99, the most Water Elementals you can summon in a single stack is 396, which only has 11,880 health, which is 3,025 less than the 14,905 damage each stack takes (and that 14,905 is before the Water Elementals' "double damage" effect). This means that the most damage Armageddon can do in practice is 14 stacks of at least 994 Water Elementals + 26 stacks of 396 summoned Earth Elementals (as 396 summoned Water Elementals don't have enough health to take even 14,905 damage, let alone twice that much) + 1 Ballista (250 health), 2 Ammo Carts (100 health each) and First Aid Tents (75 health each), and a Catapult (1,000 health) = 14 * 2 * 14,905 + 26 * 14,905 + 250 + 200 + 150 + 1000 = 806,470 damage. As a comparison, Implosion's maximum damage is 22,711.