(To proliferate, choose any number of permanents and/or players, then give each another counter of each kind already there.) Agent Frank Horrigan has indestructible as long as it attacked this turn
It continuously gives your creatures abilities and stat boosts, with the one that gives trample the most relevant as it makes many blockers irrelevant
In other TCG-related news, check out the Charizard ex Special Collection
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
It's very difficult to find a first-edition copy in NM condition, so you can expect to pay about $80 for one
Thats not to say theres no more ground for the deck to explore, of course