For issues you find with the Switch and Console releases, please follow this link and give as much detail as possible. This is the speediest way to get info to Pipeworks and get a hotfix in the works.
1.4 will bring many changes to the PC version. We strongly advise making plans to back up your worlds and players prior to updating your game. More details here.
Begin your search for Journey's End information here and here. Please report bugs and issues for Journey's End here.
For issues you find with the Mobile 1.3 update, please follow this link and give as much detail as possible. This is the speediest way to get info to DR Studios to look at your issue. Also, some troubleshooting hints here.
You should consider transferring over to a Mage because in my personal playthrough in terraria, Mage helped me all the way to the final boss. You should use (or collect) Mage gear on some of the lower tier bosses to get used to it, then slowly get to higher difficulty bosses till you're a full fledged Mage. (this is just a suggestion) good luck with your fight!!!
For the weapon against the destroyer...hm. Try to get that upgraded repeater...I don't remember the name I will recommend the name when I search it. And build a platform way up in the sky. There is a limit to how high he can fly (works for me). He would stay below me and shoot lasers at me while I shoot my Gatling gun at him. Good luck