need to find a shrine dedicated to Humbaba and donate there untill you get it LOL. If you see the map you can look for the shrine you're looking for :)
Donate (music blocks, gems, ore, food, etc) to the shrine of Humbaba. Check your current donation level and when it reached the limit shown, you'll get an emblem of Humbaba. (all eleven giants have emblems, and they're all good things to get, even if Humbaba is the one you happen to want first)
um...about donating music blocks, donate only once you've collected all of the same type (5) for each of the five music block groups... Or if you get duplicates and haven't achieved the trophy for a music block group (BB for instance), you can donate the extras (ex: you have 3 BB-1 blocks... 2 are donation fodder)
fwiw, the donation value of an item is ~1/10th of the value shown when you view that item's info tab.
also get yourself some Extremely Hallowed Shrine Powder and sprinkle a shot of this before you donate. it only works on one donation per sprinkle, so make sure you make it a good one, like lots and lots of butterfly milk, or loads of the same sort of music block. Also, check out "favor saver" to calculate what you need to donate agent86.nfshost.com/glitch/