📯 Gullinbursti – New Season 3 Hero – 4* Holy/Yellow: Thoughts, Discussion & Summon Results with Feedback

This helps maybe with your confusion.
Gullis damage is no special skill, but a status effect.
In this example it was why it can bypass taunt with ursenas reflect its exactly the same.

There is another example with roc

When ursel is active when roc fires she will reflect the sand damage back , because that is a special skill. If roc fires and ursel isn’t active all get the sand damage. If you fire ursel after that all your heroes will still suffer from the sand damage because it’s a status effect and no special skill.
Gullis special skill is healing and giving himself two statuseffects, higher tile damage and a damage to all after 3 turns. Nothing of that can ursel reflect because it’s only on himself. After 3 turns there is also nothing ursel can do, because there is no special skill only a status effect doing damage.