Elemental Monster: Online Card Game

You fight him twice in the game, this trophy is not awarded for the first time you beat him.
This game gives you a pretty good MANDATORY tutorial when you start up the game, even if you just want to play multiplayer or learned the game by playing at your buddies house you'll have to learn how to summon and win a game just like everyone else.

The game is pretty direct, you start at one dot on a map and upon completing it you unlock a new dot labeled "New" that you have to move to. You get rewarded a single random card after every match and two random cards after two out of three round matches.

At the middle of the first several chapters you'll unlock a new deck formation and upon completing a chapter you'll unlock a new jewel which will power up creatures that are of the same color as it. Then you will unlock a new chapter and receive a trophy upon starting the new chapter during the text based cut scene.

This guide I made details all your opponents cards and play field settings up to the final chapter: Elemental Monster -Online Card Game- Singleplayer Opponent Guide
For the final chapter see Elemental Master.

Doing everything else in the game up to this second fight against the Demon King is mainly just trial and error with your deck configuration and trying to counter your opponents, but for the Demon King, he uses a usually straight forward black deck. So come with a lot of non-white monsters that know white attacks or come with whatever color you prefer plus a Paintman that can change his strongest card into a type that you can do double damage to.

Due to the randomness of the cards everyone gets, you'll have to figure out what cards are good for you and what play-style works for you. You'll need to make multiple decks, some for just a single opponent. The developers give you twenty different deck set slots that you can toggle with & in the deck edit screen, so don't be afraid to experiment.

If you're having trouble in the game, try building a deck with three Gargoyles, they can be found within The Legend Begins set. Their first attack Evil Eye has a one-in-four chance of doing an insta-kill. The second attack; Curse of Death, kills off your Gargoyle and insta-kills your opponents standby monster.

His SP skill can be situational and its reverse effect is only useful against decks that use mostly white creatures. You'll need a fourth card for this deck and pretty much anything can work. The field formation can be anything, but split would be the best and the jewel color should obviously be black.