Unbound Battle Elixirs can be bought from the Shop. Battle Elixirs (Bound) are obtained by participation in the Colosseo event. Bound Elixirs are sent to presents as rewards for the accomplishment of a variety of Colosseo tasks.
Unlike other event-specific items, one of the elixir types is not bound, making it tradeable or giftable to other players. This becomes important at the end of the event for the conversion only affects only items appearing in your inventory.