SP Endurance (i.e. level 500 to 9999) focused [Kullervo] build, requires Shooting Gallery with Muzzle Flash to crowd control enemies passively, combined with Vazarin Protective Sling and Rolling Guard for i-frames and status cleanse. [Muzzle Flash] also blinds enemies and forces a 700% melee stealth multiplier (which is additive to a weapons critical damage multiplier). Note, as of April 2024, [Muzzle Flash] no longer blinds eximus through overguard.

An alternative subsume is Quiver arrow with Cloak arrow, which gives up two three 'bubbles' of invisibility within a relatively small zone, however you may want to use duration shards to increase the duration of quiver or swap [Stretch] for [Constitution].

Breach Surge also works if you want additional damage for worse crowd control.

VARIANTS

Full melee tank (lycath): https://overframe.gg/build/494127/kullervo/full-mecha-jacket-maximum-ehp-melee-tank-kullervo-lycaths-hunt/
Full nourish tank: https://overframe.gg/build/495248/kullervo/nourish-energy-tank-kullervo/
Pure ability DPS: https://overframe.gg/build/494140/kullervo/mechanized-daggers-mecha-set-pure-ability-dps-kullervo-roar-non-melee/

PLAYSTYLE

1. Keep Shooting Gallery active at all times on cooldown. Every 6 kills from any source followed by attacking with a gun or melee will trigger a 28m through wall radial blind from your current position for almost 8s. Note you do NOT need allies as an instance of shooting gallery is always active on you.
2. Tap 1 on an enemy for Wrathful Advance to teleport you to that enemy, heavy attack then gain a FLAT ADDITIVE 400%+ crit chance boost to your melees for about 12s.
3. Tap 3 for Collective Curse to curse a large group of enemies in a 65 degree cone over an almost 60m range. Attacking any of these cursed enemies with his 4 or a x12 heavy attack i.e. either manually or using 1, will transfer 100% of the damage to all other cursed enemies (only the instance of initial hit and resulting bleed damage but not the slash status itself).
4. Tap 2 to gain overguard whenever depleted to refresh overguard gate.
5. If not subsumed over, Tap 4 for Storm of Ukko to create a 23m zone of slash damage and slash procs which can deal slash damage + status to enemies, stun enemies and generate combo to maintain you at x12.

BUILD SPECIFICS

Duration
Positive duration is mainly needed for the cc buff from 1and uptime of shooting gallery. 3 and 4 both have quite long duration already so we don't need to go to excessive.

Efficiency
Neutral or positive efficiency with [Primed Flow] and arcane energize would be ideal for energy economy. If you have energy issues, consider dropping [Stretch] for [Streamline].

Range
High range is primarily for [Muzzle Flash] blind radius to make sure nothing in range can shoot you, as well as the radius of 3 and 4.

Strength
A strength threshold of 200% lets Collective Curse distribute 100% of damage so this is all we really need to hit.

Aura
[Growing Power] is used to hit the strength threshold. If you don't have an aura forma, you can just leave this for [Enemy Radar] or [Corrosive Projection].

ARSENAL

We can use Hybrid x12 heavy or x12 Heavy Spam builds best with [Kullervo]. This means you have option of both spamming light attacks and using x12 heavy attacks.

The strongest x12 heavy weapons with a forced slash proc are (in order from strongest to weakest):
1. Hate (Incarnon): https://overframe.gg/build/494117/
2. Quassus: https://overframe.gg/build/494400/
3. Tenet Livia: https://overframe.gg/build/494405/
4. Dokrahm - Korb - Ruhang II: https://overframe.gg/build/496181/dokrahm/kullervos-arsennal-pure-x12-heavy-spam/
5. [Anku] Incarnon
6. [Azothane]
7. [Pennant]

Other good options include: [Glaive Prime], [Reaper Prime], [Tatsu Prime], [Tenet Grigori], [Keratinos], [Venka Prime], [Nikana Prime], [Skiajati], [Sepfahn]

Note for each of these, when using with [Kullervo] due to his 75% heavy efficiency passive, you can remove [Reflex Coil] for [Sacrificial Steel].