Radiant Gargoyle Stoneplate

The physical-defense stat that reduces incoming AD damage. Tank items, the Defender trait, and champions or items that grant flat Armor all feed into this mechanic, alongside the handful of effects that scale a bonus off a unit's Armor value. Sunder is its inverse — a debuff that reduces enemy Armor.

The magic-defense stat that reduces incoming AP damage. Many sustain items, the Defender frontline trait, and "Gain X Armor and Magic Resist" effects grant or scale off it; Shred is its inverse.

How a unit chooses what to attack or hit with an ability. By default a champion attacks the closest enemy by hex distance and keeps hitting it until it dies or moves out of range, then retargets to the next-closest enemy. That default is why frontline placement matters: a tank parked up front soaks the enemy carry's attacks while your own backline carry is left alone. Some abilities override the default with a special selector that picks a different enemy: the lowest-Health target (Rengar leaps at the lowest percent-Health enemy nearby; Murkwolf leaps at the lowest current-Health enemy nearby), the furthest enemy (Kha'Zix leaps at the farthest enemy in range), the highest-Health enemy, or the largest clump of enemies (Gnar jumps into the largest group). Untargetable removes a unit from the pool of valid targets entirely.