Here is the full list of all 64 Widow in the Endless Labyrinth achievements.
Complete Maze X-10
Complete Maze X-9.
Complete Maze X-8.
Complete Maze X-7.
Complete Maze X-6.
Complete Maze X-5.
Complete Maze X-4.
Complete Maze X-3.
Complete Maze X-2.
Complete Maze X-1.
Acquired the skill: Invincible Barrier.
Acquired the skill: Sword Rain.
Defeat Plague.
Complete Maze 5-3.
Complete Maze 5-1.
Complete Maze 5-2.
Acquired the skill: Ameno Habakiri.
Acquire the item: Goal Radar.
Acquired the skill: Steel Stings.
Acquire the item: Invincible Barrier.
Watch the Credits scrolling until the end.
Defeat Hammer.
Complete Maze 4-3.
Complete Maze 4-2.
Acquire the item: Phoenix's Feather.
Stand with the protestors and defeat the soldiers.
Complete Maze 4-1.
Acquired the skill: Lightning Bolt.
Pass the trial of Brawny Soldier Bros.
Acquired the skill: Floating Eye.
Complete Maze 3-3.
Defeat Queenbee.
Acquire the item: Bamboo Dragonfly.
Complete Maze 3-2.
Acquire the item: Sonic Boots.
Acquire the item: Event Radar.
Complete Maze 3-1.
Acquire the item: Steel Fortress.
Defeat Lady.
Complete Maze 2-3.
Complete Maze 2-2.
Complete Maze 2-1.
Acquire the item: Shield Breaker.
Save Widow's Minions and pass the trial of ambush.
Defeat Captain Kyle.
Complete Maze 1-3.
Pass the trial of Bullet-Reflection.
Complete Maze 1-2.
Acquire the item: Aegis.
Acquire the item: Hourglass of Disorder.
Acquire the item: Sky Breaking Drill.
Acquired the skill: Huuma Shuriken.
Acquire the item: Berserker's Armor.
Acquire the item: Sonic Bracelet.
Acquire the item: Energetic Battery.
Pass the trial of Timid Man.
Acquired the skill: Omni-Slash.
Complete Maze 1-1.
Acquired the skill: Shadow Clone.
Pass the trial of Master of Anti-Stun.
Acquired the skill: Rocket Launcher Drone.
Acquire the item: Excalibur.
Acquire the item: Energy Drink.
Acquire the item: Thunder God's Hammer.