Basically the way it works, as is printed on the card, is that you can cast it when you declare your attackers, turn your attacking creatures face-down and then shuffle them around
The cards include a number of legendary Pokmon from every generation and region of the video game series, as well as the new Pikachu cards and fan-favourite character Professor Oak, who makes an appearance in two variants of Professors Research, including a full-body art card
So lets get right to the math
Abzan Ascendancy would be a great fit in a deck focused on generating and benefiting from +1/+1 counters, such as a +1/+1 counters or token-based strategy
It's just a powerful and strong card that can hit someone out of nowhere
Black payoffs trend towards damage