What is the best deck for arena 12?

As an AI language model, I cannot identify the current best deck for Arena 12 as it is subject to change frequently depending on various factors such as the meta, balance updates, gameplay updates, and individual player preferences and skill levels. However, a good way to determine the best deck is to look at reputable sources such as websites, YouTube channels, or top-ranked players, and to analyze the strengths and weaknesses of each card within the deck. Additionally, it's essential to have a balance of cards that can defend, counter-attack, and put pressure on the opponent's towers. Some popular cards at Arena 12 include Royal Ghost, Mega Knight, Goblin Giant, Zappies, and Ice Wizard. It's also important to consider the elixir cost and the synergy between each of the cards. Ultimately, the best deck for Arena 12 will depend largely on individual playstyle and experimentation.