The Fred, or Nimzovitch Fred. incorrectly named the Colorado Defense by Nimzovitch Defense author/expert Hugh Myers due to a letter sent to Chess Life by a reader from that state. Future International Master Doug Root, a friend of mine contributed to its development back in the 1970's, using it with mixed results in the old Louis Statham Master's plus tournaments he sponsored in Lone Pine, California. So, it should be called the Root Counterattack.
1. e4 Nc6, 2. Nf3. f5. I'll make some videos about it eventually, once my website is upgraded. I have a few lines that used to beat the silicon beasts, but they fixed that....
What Openings do you consider very tricky or complex?