The head of this magical silver mace has seven, evenly spaced holes to its hollow, rune-carved interior. The handle is wrapped in a silver leaf, and the short pommel chain is capped with a tiny hollow replica of the head of the mace.
On a critical hit, this weapon heals the wielder for the same damage that is dealt.
While attuned to this weapon, you may use the Word of Radiance cantrip, with a spell save DC based on your Wisdom modifier. While attuned to this weapon, you may add twice your proficiency bonus to Performance checks for singing.
QUESTION: Does the twice your proficiency bonus stack with proficiency and/or expertise?