Easily by staying out of the hole in the first place and anyways they haven't had a buried alive match in years.
The way you escape a buried alive match is like this. When you get dropped into the hole. There is a door on both sides of the grave and when you get through the hole your supposed to lose the match. Every match like that is planned by the WWE before it happens because it's fake. If you should lose the match you go through the door when your time is up to fight and there is a path under the ring. You go in there and walk under ground and wait under the ring. Down there they have water and food and a walkie talkie so they can come out when the WWE arena is cleared with all the fans so they can't see them get out.
They have a trap door that allows an easy exit and a simple way to make an intresting match more intresting and a second mini trapdoor allowed Mark Calaway (Undertaker) to stick his hand up.
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WWE does it's 'Buried Alive matches' by making the hill around it a metal casing, if you listen closely in the match at Bragging Rights 2010 when Kane and the Undertaker are exchanging blows, when you Kane is throwing a punch and stomping his feet on the floor you hear a hollow banging noise, and the when the Nexus run onto the stage you can also hear this noise.
When the Undertaker is in the grave notice you only get shots of him when the Nexus are shoveling dirt onto him but when Kane tells them too move, you don't see him at all. There is one of two ways the WWE could do the Undertakers escape one- by letting him sit in a compartment with water a monitor to watch the rest of the show on it with a WWE trainer in there with him to check him over or two- by elevating the floor (using a temporey stage) next too the grave leaving him enough room to crawl or crouch and walk. I have read through some of other people's theory's on what happens when the dirt lands on him and non of them make any logical sense. i hope i have helped answer your question.
What happens is the Undertaker is always buried alive. In the grave the Undertakers opponent has to make sure that the Undertaker is in a little room were he can have some food and drink. Then, his opponent can shove the cement back into the grave. After the event is finished, and everybody has left the stadium, the Undertaker can then escape from the grave. Also, the Undertaker is the creator of the buried alive match and is the only one who ever gets buried alive anyway, so my answer may not be accurate.
Power
I believe the first appearance by a casket in a WWE game is in SmackDown vs Raw 2006 in the form of Buried Alive match, so the answer is no.
Yes
I believe there is no such thing as Lego WWE video game. Either you made that up or someone really tricked you.
No there is no DQ or count out in triple threat matches