I loved this mechanic because it captured the trope of a villain telegraphing their evil plan
"There's the start of a nice Marchesa Commander deck in here, but it's up to you to decide how you want to play these
However, Alara is such a popular plane and Wizards constantly makes callbacks to it, I suppose they'd rather save that story for a main block instead
I won't fight you on it
While a 5/5 indestructible beater sounds like a reasonable threat at first glance, considering that Historic will likely heavily feature Teferi, Hero of Dominaria, Teferi, Time Raveler, and Oko, Thief of Crownsall of which incidentally answer a 5/5 indestructible Darksteel ReactorI'm not sure the plan will actually be competitive
Once played, these cards remain in play until you or an opponent do something to remove it