I want to run a sub panel from my main panel apx. 400' using 100amps and 2-2-2-4 wire. Is this possible or would I need to have a transformer set? I'll be using it for and entertainment forum. Running sound, lights, etc. please.

You need to calculate the voltage drop.
See
Voltage Drop Calculator

100 amps 120 volts at 400 feet requires 4/0 cable for a 5% voltage drop.

First thing you need to do is calculate or determine what the maximum amperage draw will be. That is the maximum amps that will be used at any one time. Plug that into the voltage drop calculator. That will give you wire size. Wire size will give you breaker size.