My best advice is to just use a hacked client while they are still existent for Flash and take advantage of the auto-nexus and just practice on prod itself.
(Exalt also has a few hacks released so far, but I don't trust them yet, gonna wait and sit on those until I see what happens to other people using it)
Would take a long time to perfect a prod-like Lost Halls, you would first have to set up a private server of your own on your desktop, and then also learn (assuming you're new to the process) how to implement mobs/projectiles and write behaviors for them, how to make the map and implement the map and being able to access the map, having your newly implemented mobs being randomly placed in each room of your newly implemented map, and so on.. because well a simulator for this type of thing does not exist :P
Sadly there are no public assets/code for a Lost Halls so if you go the selfmade private server route, you would have to replicate it yourself. (Well, the assets can be found on
https://static.drips.pw/rotmg/production/current/ but thats useless if you dont know how to do what I said earlier in this paragraph.)
If you don't like the hacked client advice, then you're next best bet is to play a private server with lost halls implemented and grind a trickster on the private server and then buy a Lost Halls key, usually keys are sold for fame on private servers (also assuming the private server has Lost Halls implemented)
