I just realized something, since we're talking about articles - where did Squirtle's bubbles come from? O_o
I think Ivysaur really shows how far the PMBR can push themselves when it comes to special attacks. Seed bomb uses the same basic idea of bullet seed (shoot up), but changes it significantly by keeping the attack alive until it hits the ground, giving it physics so that it starts to fall after a bit, giving it the ability to stun people if it hits them on the ground, etc etc.
And Solarbeam - I think they said that was just a huge, extended hitbox from Ivysaur's face. (oh, maybe that's how they did bubbles, haha).
So if Isaac has any moves that would make sense in that capacity, the PMBR might be able to make it work. Some people have mentioned he has Earth magic - so a possible Up-B for him might involve him summoning a pillar of Earth to push himself up. If it extends out from his model and isn't ever separate from him, then it might not need to be an article at all - it could function like solarbeam, where it exists for a brief moment while Isaac is rising, and hurts anybody it touches. Then it goes away as Isaac is launched upwards.
Again, I don't know the character, so that might be a horrible Up-B, but I think it's an example of how the PMBR can work around the article limits.