Here is the full list of all 40 Overlord: Fellowship of Evil achievements worth 1,000 gamerscore.
You completed act 3.
The plot thickens.
You defeated Sparkle.
You defeated Clarisa.
You fully upgraded one minion colour.
You defeated Cedric.
You completed act 2.
Your Greens assassinated 50 enemies
You defeated the Void Gazer.
You bought all of one character's statue upgrades.
You introduced the peasants to the zombies!
Your Reds killed 100 enemies with their explosions. Boom!
You summoned 500 minions.
You completed act 1.
Careful, we already lost one Overlord down there! I wonder what happened to him? - Gnarl
You gained 100% of the crowns in one quest.
Your minions looted 250 shiny objects.
You killed 50 sheep
Your Blues healed 500 times.
You crashed the banquet.
Your Browns killed 50 enemies.
You completed the prologue.
You bought half of one character's statue upgrades.
You summoned 250 minions.
You knocked 20 enemies off the Netherdeep and into the Abyss!
You helped Ricket fix her forge.
You completed a quest in online multiplayer!
You killed a "boss enemy" in a multiplayer game.
You finished a quest in 1st place in multiplayer
You defeated the Trolls.
You completed the tutorial.
You summoned 50 minions.
You had 12 or more minions active at a single moment.
Obtain all weapons for all characters
Gain 100 crowns in-game through winning phases
With four players, each summon 4 minions at the same time.
Complete/win 100 traversal states within the time limit
Buy all of the upgrades for all minion colours.
Buy all statue upgrades for all four characters.
Complete a quest in local co-op with at least 2 players present.