Relic
Mystic's Protection Banner
Unique
Effect
Whenever a 
Mystic casts, they Shield the nearest Hero equal to the total number of Debuff stacks on all enemies.
Where it drops
No drop source recorded in the game files.
Other Unique relics
Questions people ask
What does Mystic's Protection Banner do in Guildrun?
Whenever a Mystic casts, they Shield the nearest Hero equal to the total number of Debuff stacks on all enemies.
What is the difference between a relic and an item?
Items are equipped by a single hero and take up one of that hero's slots. Relics apply to the entire guild and do not use slots. That makes relics the stronger of the two when a build starts coming together.
How do I increase my team size?
Harmony Crystal raises it by one, up to five. So does each of the fifteen Mandate relics, but those require finishing an objective first, like dealing 15000 auto attack damage or applying 30000 shields. Pick the Mandate that matches what your team already does.