The aim of the deck is to get them to bring out a cleffa. After they do this, you use spider web over and over to lock it in place. Use Vileplume to stop them from switching. Pokemon reversal to pull up their cleffas.
Apart from spinarak and vileplume. you would run any of serperior, yanmega, RDL, etc; something that benefits from a long time for you to set up.
The strategy is to continue to lock your opponent for the whole game. When time is called, you wait until three turns pass. After the third turn ends, you can simply promote any pokemon you want and kill the cleffa, allowing you to take the first prize and win. This deck works well with Reversal, allowing you to pull up cleffa.
This deck is MAINLY Vileplume/Yanmega! the difference is the inclusion of 2 Spinarak. If you want, you can include an araidos (GC for 30 - to kill cleffa).
This isn't going to win you nationals. It will, however, be awesome.
EDIT: Going to simplify.
You play the game, and wait until time is called. After time is called, 3 more turns get taken (often referred to 30+3 or 45+3).
After the 3 turns, if both players are on equal prizes, the first player to get a knock out wins.
You stall with Spinarak until time is called, and the turns pass, then attack cleffa for 30 damage, knocking it out. You take a prize, you win.
Spinarak is also good with just vileplume and stuff, and not in a gimmick deck.