I am at lvl 29-30. Already beat the dragon but before heading up to 1on1 against Kwanda. Here's the pattern I found, which is different from the original poster's. His steps and command order didn't work for me(probably because I had beat the dragon already) so I had to spend some time figuring out my own, which ended up working and I was able to get 10 mangosh in 25 mins. (took me a few hours to figure out the pattern though)
preps: all lvl12 weapon sharpened, fire rune on Kirkis. I got one by fighting kobolds in the world map. I was lucky and got one in less than 10 battles since I left burnt village.
1) save in Burnt elves village
2) encounter exactly 4 battles in world map. Let go on all of them.
3) enter Pannu Yakuta
4) encounter exactly 3 battles, which contain different number of soldiers as already mentioned by the original poster. Let go on all of them.
5) in the 4th encounter with 1 armor and 3 shields. turn 1: falcon rune on armor, Viktor Clone on armor, Kuromimi/Tir/Gremio defend, Kirkis level 3 fire magic spell(dancing fire)? turn 2: free will. This should kill everything but I didn't get any drop after the battle.
6) the 5th encounter will also be 1 armor and 3 shields. turn 1: falcon on armor, Clone on armor, Kuromimi/Tir/Gremio defend, Kirkis level 2 fire magic(firestorm). turn 2: falcon on default target, Viktor defend, Kuromimi/Tire/Gremio attack on default target, Kirkis level 2 fire magic. The last attack in this battle will be a critical hit from Kuromimi to a shield. Mangosh as a drop after battle.
7) go to the girl and rest up.
return to burnt village. save up. reset game. repeat from step 2 again with exact pattern and so forth.
I am playing the PSN version and I only use the soft reset by pressing the Home button on my controller.