In the 1980s, when I started mountain biking, and deep into the 1990s, when I started to take it seriously, having a "mojo" on you bike was a prerequisite to YOU being taken seriously as a mountain biker.
I tried a Google search of "mountain bike mojo" and it wasn't until page 12 that I found a reference to it, beyond the Ibis Mojo mountain bike, and Mojo suspension. Fortunately, so I don't sound like a complete idiot, it was a reference to the mojo of the 80s and 90s from the "Dictionary of Mountain Biking Slang". Here is what it says:
mojo n. charm or icon worn by a biker or attached to the bike.
In the 80s and 90s, having a good luck charm on your bike almost felt like a necessity. Let's be serious here - if it was slightly damp out, you would be lucky if you could stop yourself (remember low profile cantilevers?). Suspension was still mostly a fringe thing, with the first production fork only showing up in 1989 complete with a whole host of naysayers and "suspension deniers". Reliable suspension didn't really exist until the end of the 90s, and since then what a mountain bike is capable of in terms of brakes and suspension has morphed exponentially.
So, back in the start of this thing called mountain biking, hanging some good luck, or mojo, on your bike made a lot of sense. Getting down the trail back then took a lot of luck, crazy skill and immense physical fitness (mostly for healing after you crashed).
In general, it would appear that a "mojo" is no longer a regular occurrence in the mountain bike world. In today's realm of full carbon, full suspension, multi-wheel size $6,000+ bikes, maybe the tacky bit of plastic figurine representing you luck or soul is a little dated?
Whatever...I'm going to bring mojo back. In the true spirit of mojo, the new mojo on my Banshee Prime was given to me. Take that modern mountain bike world!