In main event mode, do the following things to unlock extra outfits and characters.

Shawn Michaels DX Outfit Get Main Event Rank with Shawn Michaels.
Triple H DX outfit Get to Main Event status as Triple H
Vince McMahon bald head Win the ECW world championship

PPV Arenas - To unlock the PPV arenas, players have to play through Main Event mode and get a Title shot and then compete for the title. The PPV that the match happens at is the PPV thats unlocked. Therefore it is possible to unlock between 1-3 arenas per play depending on your choice of brands(ie. Raw and Smackdown! both have three titles to compete for while ECW only has 1, so it is best to stick to Raw or smackdown until the second time you are asked to change brands before changing to ECW in order to get more arenas unlocked).

Armageddon Compete for a title in Main Event mode while part of the Smackdown! brand

Backlash Compete for a title in Main Event mode while part of the Raw brand
December to Dismember Compete for a title in Main Event mode while part of the ECW brand

ECW One Night Stand Compete for a title in Main Event mode while part of the ECW brand

Judgement Day Compete for a title in Main Event mode while part of the Smackdown! brand

New Years Revolution Compete for a title in Main Event mode while part of the Raw brand
No Mercy Compete for a title in Main Event mode while part of the Smackdown! brand
No Way Out Compete for a title in Main Event mode while part of the Smackdown! brand

Royal Rumble Compete for a title in Main Event mode while part of the Smackdown! brand

Summer Slam Compete for a title in Main Event mode while part of the Smackdown! brand
Survivor Series Compete for a title in Main Event mode while part of the Raw brand

Unforgiven Compete for a title in Main Event mode while part of the Raw brand

Vengence Compete for a title in Main Event mode while part of the Raw brand

WrestleMania Compete for a title in Main Event mode while part of the Raw brand

Unlockable Characters

JBL Gain Main Eventer ranking in Main Event mode for the SmackDown brand

Shane McMahon Gain Main Eventer ranking in Main Event mode for the Raw brand

Unlock Tommy Dreamer, Roddy Piper and Sabu Do Main Event Mode as anyone and get to Showstealer

Vince McMahon Gain Main Eventer ranking in Main Event mode for the ECW brand