It's very cheap, but you could put a Lot of weak monsters in your deck and all the spell cards, that decrease a few hundred life point. You just Set all your monsters and wait until he summons Ra, then use a spell. He will most definitly sacrafice his LP as otherwise Ra is useless.
I ran 3 kuriboh multiply and detonate took me like four tries to finally get a hand that works. Basically Marik has to start you did a kuriboh multiply detonate and a monster
If you draw E-con, you can just steal his Ra, use effect to destroy any monster he may have summoned, then attack directly with Ra for easy win (this assumes you go second). If you go first, you'll need something that can stall Ra for a bit.
Use Pegasus, and battle until in the first turn you invoke relincshed and use the effect in RA, in mean while you need invoke another creature to beat his monsters but not necessary in the first turn, it´s only to you remove Ra from the battle and increase your chance of victory