yep, for full casual players, the dungeon bosses, extreme trials & normal raids are too difficult (for us HC & semi-HC its ofc not too difficult)
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the fights should be fun & engaging and not necessarily just "harder".., yes, you can make fun & engaging battles & content in mmos, without making them just harder.. (Yoshi might need a fresh perspective & hire some fresh talent for such content, but definitely keep the talent he already has for HC / semi-HC designers)
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the bojza battles were more fun / engaging than difficult, those should maybe be indicators, on how too keep fights fun, not harder