0. Make sure to keep a safe backup before you perform any edits.
1. Make sure you already defeated the champion on your B2W2 save, and have access to Black City/White Forest.
If you didn't, go ahead and defeat the champion
2. Download the Generation 5 tool.
3. Load up your save in the BW Tool, open the 3DS Link (Dream Radar) tab.
4. In the window, make sure Legit Mode is selected, set Landorus to the first legendary slot,
and Save and Exit.
5. Proceed to Update Checksums and go ahead and Save.
6. Proceed to load the save. In the Continue screen > Unova Link > Nintendo 3DS Link
7. Proceed to Receive research data
8. You've received Therian Landorus
9. Once received, fly to Black City/White Forest, and make your way to the Abundant Shrine.
You will need Surf and Waterfall to get there, and bring the Therian Landorus. The NPC should be there.
(if you're already in the Abundant Shrine, you need to exit and re-enter to reload the area for the NPC to load)
10. Talk to the NPC, receive the Reveal Glass.
The Reveal Glass received works!