Is 70 mini bosses too much?

[byrdbones]

If your game is huge, and you have lots of explorative/secret areas, then why not!

 

[xspec]

I think it depends most on how you implement the feature. If they're challenging and offer good rewards, then a player might not get tired of them. If they're hidden and require some sort of puzzle to be completed beforehand, that could also make the encounter more exciting. I think the difficulty of the mini-bosses should also vary widely, making each encounter more fresh, because otherwise they just turn into a repetitive 'beefed-up enemy'. You could also offer rewards based on the number defeated, or have certain mini-bosses unlock only after a certain number are defeated, or have certain other optional events unlock... it's really up to you.

Relative scarcity of the mini-bosses should definitely be a consideration though, because if the player fights too many of them in a short span of time, it stops being a dangerous, exciting encounter, and more of a "Oh look, it's one of these things again". Since you have 7 main bosses, that means your player would basically fight 10 mini-bosses per actual boss, which is a little high. Maybe scale it back to 3-5 mini-bosses depending on the time between each real boss.