In Arena, when creatures enter combat, their avatars visually clash together with a battle sound effect. The game enforces the rules, but it also shows you why things happen as they do. “When we started on the project four years ago, we had very limited client visualization capabilities,” says Reiff. “If you wanted to know what happened, you had to read the card. The card was on the battlefield, then suddenly it was in the graveyard and you had to figure out why.” Arena set out to show players why those things happened with animations and guide lines. If a card in play prevents you from casting a spell or taking an action, it will flash red to show you why. In a real-world game, you might forget and breeze right by it without noticing. Worse, it could count as a rules violation in a competitive tournament and earn you a costly penalty. Arena simply won’t let it happen.