Without a doubt this will be the biggest test of Jacare's young MMA career.  Mayhem is a tough, scrappy kid who has been in this game for a while, around seven years to be exact.  Ronaldo Jacare has fought relative unknowns in his dominant wins, and Jason Miller has fought big names in George St. Pierre (decision loss), Frank Trigg (TKO loss), Denis Kang (RNC win), and Robbie Lawler (Arm Triangle, win).

Stylistically, however, this is a bad match up for Mayhem.  Miller is a fighter who dominates his opponents positionally, and submits them as most of his wins go.  Unfortunately this is where Jacare not only shines as well, but excels.  Jacare is a 2x open weight class Brazilian Jiu Jitsu Mundials champion as well as an ADCC champion.  Jacare has world class takedowns to match with his heavy, powerful Jiu Jitsu top game.  Jacare's grappling is tailor made for MMA.

What we have not yet seen from Jacare is his ability to strike (his first fight was a long time ago), and it is doubtful we'll see it again in this match.  To defeat Jacare, Mayhem needs to defend the takedown and punish Jacare with his striking ability.

Can Jason "Mayhem" Miller accomplish that in my opinion?

Not a chance. 

Ronaldo "Jacare" Souza wins by TKO or submission in round 1, from the mount or back.