Here is the full list of all 41 Majin and the Forsaken Kingdom achievements worth 1,000 gamerscore.
Defeat over 30 enemies with traps
Raise Friendship level and Tepeu's level to max
Defeat 300 enemies with combination attacks
Defeat 50 enemies with sneak attacks
Defeat over 10 enemies with a purification finish attack
Defeat over 10 enemies with a flame finish attack
Defeat over 10 enemies with a wind finish attack
Defeat more than 50 enemies with finish attacks
Defeat over 10 enemies with a lightning finish attack
Defeat 5 or more enemies at once using a finish or combination attack
Go to the true ending
Defeat the "Creator of All Darkness"
Get all costumes
Open all Treasure Chests
The Majin's "purification" ability rises to maximum
Defeat over 500 enemies
Help the Majin out when he's in trouble 30 times.
The Majin's "strength" ability rises to maximum
The Majin's "flame" ability rises to maximum
Get 3 full costume sets
The Majin's "wind" ability rises to maximum
The Majin's "health" ability rises to maximum
Talk to the Majin 100 times.
Help the Majin out when he's in trouble 10 times.
Defeat Ixtab
The Majin acquires "purification" ability
The Majin's "lightning" ability rises to maximum
Defeat Tlaloc
Give the Majin more than 500 orders
The Majin acquires "flame" ability
Feed the Majin over 10 Blue Fruit
Have the Majin revive you 3 times.
Attack shielded enemies 100 times.
Defeat B'alam
Become "haunted by darkness" 10 times.
The Majin acquires "lightning" ability
Defeat over 100 enemies
Defeat Caprakan
The Majin acquires "wind" ability
Escape from the Dark Castle
Save the Majin