First join map do the preevent try your best to collect all the materials but dont ever submit it in. After 10 minutes when the boss is half hp, get out of combat, and port out of the map. Port back in and complete pre event and get crystalized done.
The longest worth while most difficult legendary precursor to get is obtainable. Battle against all odds my friends from ArenaNets codes, to gw2 economy, and even against gw2 players.