Special boss?

[Potatogod]

Does anyone know why sometimes there's some special boss spawning in the map and what those are, when i open trade marked on the farm i see peoole talk about krunch II or something like that, i can remember when i played this game a few years ago and saw those bosses but didn't know (still don't know) what the purpose is of those bosses, i played recently a lvl on rockhorn summit and saw a boss like that

[Giasakes]

They give aps

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[Saint Jaffo]

Those bosses give APS. Respectively Elusive Four and Evasive Six achievements, together they form the Twisted Ten. Every player running for seasonal leaderboard (including me) searchs this special bosses as they are needed for the points. They do not spawn that frequently, that's why people sell spots for joining the map and killing them.