The two main sources of damage reflection are as follows.

Defensive item Hide of Nemean Lion: Reflects 20% of incoming basic attack damage to the attacker as magical damage.

Goddess Nemesis's shield: Reflect 30% to 50% of incoming damage with a temporary shield up, which ranges from 100-500 shield health.

Select Nemesis with Hide of Nemean Lion and use your damage reflection when enemies engage you at low health. Your ultimate can remove up to 50% of their current HP and also reduce their protections.