There are a bunch of cards that begin with: "Roll 1 die" and end with "then discard this card" but are worded in such a way that it's not clear if the discard always applies.

e.g:

Mischievous Devil (Blood Moon)

Roll 1 die:

1-2) You must give one of your objects to another character of your choice

3-4) You must ditch one of your objects at random

5-6) Take one object of your choice from any character, then discard this card

Is it always discarded after resolving the roll? or only on the roll of a 5-6?

The Deranged Alchemist is another example, where the discard is only listed under the roll of a 6 but seems like it should always apply.

If that is all the text, and written that way, then I would say only a 5-6.

Both of the cards you mentioned are exactly as written. The best things to happen are the times it gets discarded. It appears as though you are overthinking it!

The card is only discarded if you roll a 5 or a 6!

Some Events are like this too. For example, the Tumbling Boulder from The Highland says to discard it only if a specific number is rolled.

There has been some debate over whether Events should always be discarded once their effect ends, even if you don't roll a number that specifies to "discard." I personally think such Events remain on the board for two reasons...

1. Every Event reminds you to discard it (like how all Enemies say they remain until killed). So if those words don't appear under specific die rolls, it might mean it really doesn't want to be discarded.

2. Lingering Events stay on the board until their effects end (eg Blizzard) and then specifically tell you to discard it at that point. Likewise, maybe in cases like the Tumbling Boulder the effect only ends when the card specifically tells you to discard it?

Food for thought!