Easy but Not so EasyG 50

See the solution for Pandemic God. Simply play one of the games on Normal difficulty (listed as introductory here in the achievement, but this is awarded for beating a game on Normal difficulty - the 3rd highest). The same method used to grind to 100 games is also used to win a game on Heroic difficulty, so it will work for this as well.

Difficulty achievements do not stack, you will need to specifically play a game on Normal.