Building to the greatest strengths of a commander, even in unexpected ways (see also: infect) can make a deck shine and even become one of our favorite decks to pilot
That said, while Altar may be limited by the assassin creature type, there are very good ones in Mardu colors, like Vein Ripper or Thorn of the Black Rose, that can impact the flow of the game
Eris also has flying and prowess, but the most important thing is: Once it's on the battlefield, whenever you cast your second spell each turn, it creates a 4/4 red Dragon Elemental token with flying and prowess
However, the most satisfying way to find these beautiful, valuable centerpieces of the Pokemon TCG is through pure luck during a pack opening
Now, thats OP
That being said, the default deck list is absolutely fine for casual play, and very straightforward and fun to use, so a top-half position for this deck feels fair