EDIT:
Left-top at the silver ring they also spawn. I think in a better quantity since they spawn from all sides instead of only from the bottom. Try to max out your character abit before going there and farm. From like 15 minutes the map gets pretty hard but at the left top, those enemies don't spawn. So my guide would be as followed.
Grab a strong, fast character like Queen Sigma.
Grab the items from the bottom and reroll for weapons/ passives you want, but dont pick the items that are in the map.
Items on the map:
Duplicator
Chandalabore
Silver ring (cant be gotten during level up)
Gold ring (cant be gotten during level up) - Get it, increased enemy frequency
Left shroud (cant be gotten during level up)
Right shroud (cant be gotten during level up) - Get it, increased enemy frequency
Stone mask (optional, maybe for a evolve)
Spinach (can be used for evolve but increases damage output. So i would say get it.)
Pummoria (heart item, optional. Can be used for a few evolves)
Wicked Season arcana is nice. Rest is pretty optional