Defeat Wicked K.

*Missable*

You must complete all 100 Waves in one sitting to reach Wave 101 for this achievement. Make sure that you load your Crucible run on a save where you've defeated Wrath (the Scar battle) otherwise Targon will stop your Wave progress avoiding this achievement completely. Be sure to have these enhancements equipped to the weapons noted as they're proven to be very useful during my Crucible run.

Balanced Chaos (+6% Damage from this weapon returned as health, +200% Havoc Form duration) Equip on Barbs of Scorn.
Balanced Obscurus (+50% Havoc generated with this weapon, +25% evade invincibility window) Equip on Lance of Scorn.
Balanced Fafnir (+100% damage reflected back to attacker) Equip on Mallet of Scorn; not needed to attack to generate as it is a passive.
Balanced Leviathan (+96 health regenerated per minute) Equip on Salvation; not needed to attack to generate as it is a passive.

If you have yet to find any of these enhancements, please follow this thread for their specific locations.

Once you've beaten Wave 100, Targon will give you your final reward and offers you to one last challenge. Use the Bards of Scorn to traverse to the fighting area. Use this strategy: use Storm Wrath ('LB' + 'RB') then go Havoc mode ('LB' + 'RT') to work on Lord Killington's first stage of health. Once his health reaches 50%, he will split into multiple versions of himself as this animation-scene will reset your Havoc mode. Just use the Wrath shard and a Havoc shard method again to finish him off. For your trouble, he will give you a Wicked Adamantine which will allow a weapon to be upgraded to +11 if already maxed at +10.

Remember, it's ok if you've died but used an Undying Shard as it triggers automatically, this will only impact your score overall and not the achievement. Also, you will not get a score penalty if you used Nephilim's Respite ('DPAD UP').