Lomion.de, the online Monstrous Index of all 2e monsters, is currently down. In lieu of it being missing: Where can I find a complete online index of all AD&D 2e monster entries compiled on one site that is still up and functional at this point in time?
Lomion.de is archived
You can access an archive of Lomion.de on the wayback machine. I clicked several monsters randomly and their individual pages also seem to be archived (I didn't find any that were not)
This may not be ideal since some things may be outdated or missing but it seems to be a possible solution.