These are variants on idiomatic expressions.
1. Blood, sweat, and fun.
– this is a humorous variant of "blood, sweat, and tears", which is a) the name of a 70s soul group b) a popular version of a phrase in a speech by the British wartime prime minister Winston Churchill ("I have nothing to offer but blood, sweat, toil and tears").
"Blood, sweat, and tears" denotes dedicated and persistent effort in a particular cause.
"Blood, sweat, and fun" denotes the dedicated pursuit of pleasure, perhaps.
2. Flesh and brains.
– this is probably a semi-humorous version of "flesh and blood". It's difficult to know what it means without more context, though!
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