Sometimes, Magic: The Gathering misses out on keywording older cards.
Back in 2021, Innistrad: Midnight Hunt introduced the keyword ability called decayed. Essentially created by Magic R&D to get more zombie tokens out there, the low cost and build up of it meant that a player could more easily create a zombie horde. They can't block, and when they attack, they need to be sacrificed at the end of combat.
It's rather simple, really.
However, only five cards ever got the keyword and it soon went out of fashion following Midnight Hunt. To date, it hasn't been seen since.
But the thing is it had been seen before 21 years earlier, but no one at Wizards of the Coast (at the time) knew that they had done it.
The 2000 expansion Prophecy featured Keld, a warrior nation centered on Dominaria. One of the cards in the set was Keldon Battlewagon. An 0/3 creature for five generic mana, it could pack quite a punch through many early plans.
Here's the thing, though. Keldon Battlewagon can’t block. And, when Keldon Battlewagon attacks, you have to sacrifice it at end of combat. Plus, you have to tap an untapped creature you control in order to increase its power -- almost like the crew ability before crew was a thing.
As for that first half, it was decayed in all but name. In a nutshell, that's because WotC R&D wouldn't come up with the keyword for a few decades. And, while longtime players might have noticed the similarity with the Midnight Hunt mechanic, newer players probably had no clue.
It wasn't the first time, and it won't be the last time something new had already been done in Magic, but it is one of the more noteworthy because of the sheer length in time between the two. Plus, it could be re-keyworded in future printings, as many cards have been errated in years past -- especially if decayed makes a return at some point in the future.
