So I finally encountered one of those "invisible Nidalee spears."

All I can say is that it's boards hyperbole at its finest. I've experienced invisible Braum Qs and invisible Mundo Cleavers in the past, so I kinda had an idea what's going on, but the boards were leading me to believe that the spears were completely invisible, not just the projectiles themselves, but particle effects and all. One more reason for you guys and gals to never believe what you hear on the internet. Nidalee's spears themselves are invisible sometimes, yes, but you can still see the particle effects of the tip. So you can still react to them (albeit unable to in certain situations, such as when completely concealed by fog of war, but when's the last time you were able to dodge a Varus arrow from there when you were at 10% health?) However, the Mundo cleavers have no projectile effects whatsoever, and if they do (CORPORRAAAAATE MUNDO!) they're so limited that you can't tell until it's too late.

Nidalee's spears may be anti-carry weapons of death topped with nuclear warheads and herpes, but even if they're invisible, you can still see the particle effects at the tip and dodge them. Meanwhile...

Mundo don't know anything about these invisible cleavers. Sometimes Mundo get so excited about throwing them, he throws them with such force that even when they're not there they hurt people. Has happened before. SLUUUURP!

Edit: Before you boards circlejerkers start soaping yourself into a spoogy lather, I'm not saying that Mundo's is inherently worse (besides them being COMPLETELY invisible, not Nidalee spears "invisible") nor am I saying that they both shouldn't be fixed, but you should think carefully about the way you word things. Invisible spears =/= invisible projectiles. When the particles are still visible, it sucks and should be fixed, but does not warrant disabling Braum, Dr. Mundo, or Nidalee.