Fully configurable: set champion, level, items, and abilities for the attacker and for each defender. Base stats auto-scale from Data Dragon; use the manual modifier fields for passives/abilities that grant extra stats (e.g. bonus armor from a shield ability).
Ability/item damage numbers are seed examples and may lag the current patch - verify against in-game tooltips. See execute threshold and other terms by hovering.
Pick a champion to load abilities.
Equip an item with an on-hit effect to configure this.
Pick a few candidate items to see which adds the most combo damage vs Defender 1, on top of the attacker's current build/abilities above.