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