That's not once per game
Another perfect example of this is Isshin, Two Heavens As One, which reads: "If a creature attacking causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time." This is an incredible ability to have on a commander - and building a Commander deck around it is sure to be a blast - but in a Standard set it just feels off
The player base directly influences the value of MTG cards, whether you like it or not
Even within Universes Beyond, the product isnt guaranteed, and there's no reason they can't be used for future in-universes sets, either
MB : I was getting no traction with paperback book cover work
To keep from amassing too many cards, the five-card hand limit is instated, and any cards that would be discarded at the end of the turn beyond this limit are exiled