Yay, time to downgrade! I took a look at the Phrozen Keep, and the only Boss Mod's I saw were for patch 1.10 and under.
Google the Phrozen Keep, then scroll down on the left, look for "Mod Archive" under the File Center section, and you can search for the boss mod you wish. You'll need to downgrade at least to 1.10 to be able to play the mod, and you can find out how to do that as well on the Phrozen Keep (
The Phrozen Keep - View topic - From 1.11 to 1.10 in two easy steps ).
Best of your luck with getting the boss mod you want, and if you actually do downgrade to 1.10 and do all of this, you'll be able to feel like most actual d2 mod players (those folk realize that only a couple of mods work on 1.11, but all 1.10/1.11 mods work on 1.10).
~moved to mod section; hacks are dirty, mods aren't :-)