Cooperative Caster

Foundational to the magical practices of exclusive groups like of the Red Wizards of Thay, the Witches of Rashemen, and even fueling the grand rituals of Elven High Magic is the concept of multiple casters participating in a single working.  Arcane casters may take this feat represents training in casting spells in a cooperative fashion, representing induction into one of these magical conclaves.  This training provides extra insight into how others cast spells (e.g. styles of somatic or verbal components, the use of various arcane foci, etc). 

Requirements: Arcane Caster (Bard, Sorcerer, Warlock, or Wizard)

• Increase your primary spell-casting ability (Charisma or Intelligence) by 1, to a maximum of 20. 
• You may use an action to willingly lose one or more spell slots to increase the next spell cast by another player or NPC who also has this feat by the number of levels equal to the number you've lost.  Unless itheother stated, this cannot make the spell exceed 9th level (9 total spell slots used per spell)
• You have advantage on Arcana checks (Intelligence) to identify any spells you see cast.