How about rare powerful bosses where spawn is random like Shangri-La frontier,I am a huge fan of that anime
#Rare powerful bosses
rain moat
rain moat
If they add this feature, it must link with story so players will face it eventually to complete story
thorny vapor
it would be interesting, sounds like you got a shiny pokemon or something
sounds like a boss the devs just could change its color or some parts of the skin and its level, like you got a Boss that is known from the main story, and that boss has some HP/skill sets, but that rare powerful boss could have more level, more hp, or some weird patterns, and a rare spawn probability, another alternative could be make a chimera made of some bosses and make this rare boss an "anomaly", yeah it sounds promising
finding those bosses could be a reward on their own
rain moat
Totally,more like shiny legendary Pokemon rarity