One effect happened to one stack, and another effect occurred for the other stack
In Crimson Vow we saw the main-set return of a mechanic originally seen in 2015s Dragons of Tarkir set, and it's come up on rare occasions since: exploit
When his last card - Jared Carthalion, True Heir - came out in Commander Legends I wrote a whole piece about an all original frame deck featuring him
The card has since been reprinted a number of times, but never into a normal set, only as a part of a deck, as promos and also this was the version they used in Chandras spellbook
If your commander is mutated into a pile then the merged creature does commander damage and counts as your commander regardless of its location in the pile
You start with just 30 cards each containing simple, basic characters