Give Spong some take down defense or defensive wrestling skills and he would be a major, major threat to everyone in MMA.
Give Jussier Da Silva some take downs and offensive wrestling and he would be nearly impossible to beat.
Same thing for Werdum, give him some offensive wrestling and he would be tough to beat.
Mark Hunt would be one tough bastard if he had defensive wrestling.
If Phil Davis had some kickboxing or just about any striking ability he would be amazing.
If you could give GSP more aggression or tenacity then he would be the best fighter ever.