Min(imum) Damage is always inflicted, regardless of Armor, whereas Normal Damage can be reduced by it. Thus a fully upgraded Archer (8 Minimum Damage and 5 Armor) always inflicts 8 damage even on a fully upgraded Grunt (6 Armor), whereas the Grunt's damage is reduced from 14 (1 Minimum and 13 Normal Damage) to 9 (14-5) against the Archer.
Catapults always inflict 255 damage with a direct hit, and 63 (1/4) damage to any units in the eight adjacent squares (structures are only hit once, but adjacent units may still be damaged depending on where the structure is hit).
|Rain of Fire
||9||Tower||1500||140||Rain of Fire||9|
||11||Tower||3000||140||Summon Water Elemental|