Endless Potion of Potency

Once per day, as an action a creature may drink
from this magical potion to gain added potency
in a specific spell damage type (acid, cold, fire,
force, lightning, necrotic, poison, psychic,
radiant, or thunder) for 12 hours.
All spells cast of the chosen damage type gain
1d4 damage for every 2 spell slot levels used and
the added effect is doubled on critical hits.
Level 1/2 = 1d4 — Level 3/4 = 2d4
Level 5/6 = 3d4 — Level 7/8 = 4d4
Level 9 = 5d4