Emissary Green seems overcosted at five mana for a 3/3 that must attack before you get any benefit, either Treasures or +1/+1 counters depending on how all the players vote (you should vote security yourself to boost Emissary Green large enough to survive combat)
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UR spells itself is often known for having a bit of an Identity Crisis, as it often ends up in an awkward spot between aggro/control
Since board sweepers are so rare in the format, it actually fills quite a sought-after niche
They arent a tribe in any sense and are really just cool creatures to include in a Kenrith, the Returned King deck, which is exactly what I have for you here
It is a 3 cost blue enchantment that allows you to draw a card each time an opponent casts a spell, unless they pay 1 mana to stop you doing so