The set 4 Magic cards based in Fire, Blizzard, and Thunder are now labeled Magic/Attack.

Does Sea Neon prevent these now?

Accordin to the rulebook, no. They're merely magic cards.

The 'attack' part of it is to imply that you'll be able to use them in a challenge to increase your player's current attack by whatever it casts. Same rulin they had in the first set that everyone overlook'd. We've even the question in the comprehensive rulins post.

Hope this helps!