Does boss bonus work for items from extra slot?

Question

If I boost bosses like Tyrn, Ocyakao and Shlorg, the boss bonus will work to Sun Mirror, Eye of the Storm and Glass of Goo?

Answer 1

Yes, this is confirmed through double Soulforged Lantern drops on Pale Worm mini-bosses.
The lantern actually doubles as a light source and can be equipped in that extra slot.

Based on that - you can safely assume that yes, all of those items would be affected too.

Comments

this logic also apply for bp right?

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yep
backpacks are affected too

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That is great to know! I never really put Ocyakao in bonus slot >.<