Hey fellow Diablo player! When it comes to defeating bosses in the campaign, it’s all about knowing their mechanics. Make sure to have resistance gear for specific elements, and always keep moving to avoid their attacks. For optimizing gear, focus on getting items with stats that complement your build. Don’t forget to upgrade your gems and enchant your gear for that extra boost. As for leveling efficiently, prioritize completing main quests for big XP rewards and tackle side quests for additional experience. Also, consider running bounties for extra loot and experience. Good luck out there!