I recently managed to get my greedy little hands on Deathbringer's Will. Since having it I have discovered a few things that future users should be aware of.
1. All other dps (save casters) will either hate or envy you. Learn to live with it.
2. You have no control over when or what shape shift will occur. So yes this trinket WILL make you look fat.
3. Shape shifting into a Vrykul will make you unable to use mounts until you remove the buff. (Taunka and Dwarf form seems to works fine.) There is a simple macro you can add to deal with this issue.
#showtooltip mount(s) of choice
/cancelaura Agility of the Vrykul
/cancelaura Speed of the Vrykul
4. The shifted shapes are ALL male so if you play a female character you will see your gender specific titles spamming every time you shape shift.
5. Sometimes as the result of the shape shift you will notice it appears as if your weapon is missing. It is still there but for whatever reason not visible. DON'T PANIC!
6. This trinket can proc off of Sap WITH OUT BREAKING STEALTH. Yeah I know, not really a hazard but good to know and even funnier to watch since the idea of a Tauren or Vrykul sneaking is completely foreign.
7. Shape shifting can cause distraction.... DANCING TAUREN ROGUE!!! (Ok, maybe just for me but I laugh every time I turn into a Taunka and prefer it to the Vrykul procs since I get to do the Peanut butter Jelly dance.) I have also had group members freak at finding a "Tauren" in their Alliance dungeon.
8. Shape shifting changes your size, this will effect your positioning, especially if you proc while casting Killing Spree. (Poor Gnome rogue friend of mine got stuck when he transformed into a Taunka.)
9. If you are trying to judge when this trinket will proc it appears to have a 105 sec internal cool down with about a 30% proc rate. (Again not a hazard but good to know.)
10. Rogues do NOT get the Iron Dwarf proc which gives Armor Pen. (Cry)