Support Boost (5e Feat)
From D&D Wiki
Prerequisites: ability to cast at least one spell
When you effect an ally with a positive effect through a spell, (this includes shielding, healing, or buffing attacks), you may boost an allies damage by a die value and die amount, (if they would do 1d8 of damage they instead do 2d10). If you affect someone more than once in a turn then this effect stacks as many times as you have done the effect, (if you heal someone twice in a turn and they deal 1d8 of damage normally, now they 3d12 of damage). This effect can stack if you take this feat more than once.