I got the same Ottus mish, the hill in question is outside of Foremans area and to the left, big yellow plants on the hill. I got the same mish on my 200 Froob and 194 Sloob and can confirm the reward is xp, didn't notice on the froob cause xp is no good to me but got 20M xp on the sloob.
You just run up the hill and they spawn, so be buffed before you go runnin up that hill
Edit: More like 19M xp, bad at math ><