I have also seen that neopets have been putting up either jade ss or thyoras tear (or any other silmilar one use item) on the new challengers. I think the difficulty is based on how strong (I mean the strength and defense boost of the 1p challengers, and not the difficulty, but I think they should add something like stars beside the difficulty number).

Like Kasuki Lu with 38 difficulty would be given 5 star difficulty because he has a powerful weapon and can full heal, while Jelly chia who has 120 (or 150?) difficulty given 1 star difficulty because he can only use up to like 6-7 icon weapon and usually uses weapons that doesn't do anything.