Well its pretty self explanatory, if I cast fireball and use fury of the small, do I apply the damage to one char or to all of them? By RAW what would be the scenario? Cause the trait says:

Fury of the Small

When you damage a creature with an attack or a spell and the creature’s size is larger than yours, you can cause the attack or spell to deal extra damage to the creature. The extra damage equals your level. Once you use this trait, you can’t use it again until you finish a short or long rest.

It doesn't say that it's like a spell targetting one creature but just A creature. Also its not a spell attack but just a spell.

Ahh cool cool thanks