Season 11 Sett is different from Season 10 Sett. Sett in Season 11 would rush Blade of the Ruined King as his first item, although the Sett of Season 11 rushes one of 4 mythic items. Choose between Stridebreaker, Trinity Force, Goredrinker, and Divine Sunderer.

Stridebreaker (Engage)

Stridebreaker is a very powerful item. The active is that you lunge a short distance and deal 110% of your attack damage to nearby enemies, slowing them by 60%. It also gives a good amount of health, attack damage, and a small amount of attack speed.

Trinity Force (Dueling)

Trinity Force is a powerful item, with high amounts of damage and a good amount of attack speed. The sheen effect is what really makes this item so good. It does a lot of damage to squishy targets, but less to tankier targets. If they have two or more tanks, build Divine Sunderer instead.

Goredrinker (Survive burst)

Goredrinker is a good item, especially when the enemy team has a lot of burst. It has a similar active to Stridebreaker, in that you deal damage to nearby enemies. Although, you restore health equal to 20% of your attack damage plus 12% of your missing health for each champion hit.

Divine Sunderer (Anti-tank)

Divine Sunderer is Trinity Force, although it is way better against tankier enemies. If you were planning to build Trinity Force, build Divine Sunderer instead if they have two or more tanks.