The 100-card singleton nation of the game is supposed to increase variance, especially when spread across four players and their unique decks
The other thing that is good about this card is that it does not really need a build-around at all
When it attacks, players flip a coin, and if the coin lands on heads, players can discard an energy card from the opponent's Pokmon, which makes Goldeen a disruptive option for slowing down the game if the Festival Lead game plan falters at any point
One of the better recursive dorks on defense and also a mild boost to any discard outlets you might have
It becomes a Treefolk creature with haste and base power and toughness equal to Woodcaller Automaton's power and toughness
There are a ton of common cards that gain you life when a creature enters the battlefield, so you can get a ton of triggers off of just one Cat Collector trigger