Spellweaver Helix triggers, causing you to cast a copy of Coveted Prize without paying its mana cost.
Resolve the copy of Coveted Prize, causing you to search your library for a Dragon's Apporach and put it into your hand, and then cast Dragon's Approach without paying its mana cost.
Repeat from step 2 until you have cast every Dragon's Approach in your library.
Resolve a Dragon's Approach, dealing 3 damage to each opponent, and allowing you to exile it and four other cards named Dragon's Approach from your graveyard to search your library for a Dragon creature card and put it onto the battlefield.
Repeat step 5 for each remaining Dragon's Approach.
Results
Cast every Dragon's Approach in your library and hand without paying their mana costs.