And then you can swing with Sephiroth, kill Aerith anyway, draw a card, and dump the counters onto him
Not only have they been through a lot of giant apocalyptic events before (see above), but this isn't even their first Phyrexian invasion
Thicc Blastoise will get your opponent, and possibly you, wet with Soggy Bottom or slap Hydro Hams with an enemy Poket monster
Thoughtseize gives the user an insight on the most likely play patterns for the upcoming turns, and can be used proactively to either discard an answer to a threat, disrupt the opponents curve, or strip a vital combo piece out of the opponents hand
Their ability to switch in monsters from the hand onto the field removes the targeting aspect, thereby negating the effect outright
Also, the fact that Flaffy is easy to access via Level Ball and the new stadium Stormy Mountains will for sure make it a good engine for different decks