It's clear to anyone playing that the roll for the Otherworld Horn is not a standard d20. It is heavily stacked toward the lower end. Rather than suggest is a flat 5% for each number 1-20. Why not provide something more honest? Something where the chance of getting the highest value actually matches what's expected (d100 for 1% chance),(d1000 for 0.1% chance), etc.
It just feels dishonest reading the '15-19 =epic, 20=legendary'. Using a d20 suggests we should be getting epic or better 25% of the time. Why not be honest and just say something like 100= legendary, 90-99=epic or large essence, 75-89=rare or medium essence, 50-75=common or small essence, 1-49=tiny essence. Just be honest with the chances players actually have.
The animation only shows one number at a time, so it doesn't really even need to change.