The main difference between the difficulties is the health of enemies: enemies have less health on Casual and more health on Veteran, compared to the numbers displayed in the in-game encyclopedia. In the first Kingdom Rush the difference is always 20% less on Casual and 20% more on Veteran. The only exception is Vez'nan, who always has 6666 health in his demon form regardless of difficulty (his health in human form is still affected normally).
Difficulty also indirectly influences the enemies reanimated from graveyards. Enemies with less than 300 health are reanimated as Skeletons, and enemies with at least 300 health as Skeleton Knights, so:
- Dark Knights (240/300/360 HP) are reanimated as Skeletons on Casual, and as Skeleton Knights on Normal and Veteran.
- Demon Spawn (200/250/300 HP) are reanimated as Skeletons on Casual and Normal, but as Skeleton Knights on Veteran.
In addition, difficulty also affects the speed at which heroes gain experience: the XP gain is slower on higher difficulties. Because of this, in Frontiers and Origins, it is recommended to train heroes on Casual instead of Normal or Veteran.
The achievements Great Defender, Heroic Defender and Iron Defender can only be obtained on Normal or Veteran. Supreme Defender can only be obtained on Veteran.