Blue
Ravenous Bugblatter Beast of Traal
Not a bad idea, although I think that if you're going to allow casters of different power sources to use scrolls of spells that aren't usually available to them, you may as well throw it open to non-spellcasters as well.
Probably make it an Arcana check, even for clerical or similar scrolls. Hopefully the rarity of scrolls will prevent it becoming almost a must-have as UMB became in 3.5/PF.
What sort of difficulty do you think, and should a failure destroy the scroll, or just prevent retries?
Hmm, this is fun. Let me play with it a bit.
Let's separate into Arcana and Religion for the different power sources, just because this way the right skills are always on your list. YES, this greatly favors wizards because these are INT-based skills. Other classes now have a reason to boost INT.
Let's increase the DC, and then put some modifiers on it. How about:
Advantage if it's on your spell list or you have the Use Magic Device feature (rogue)
Disadvantage if you don't cast spells of that power source.
(So a cleric would have advantage for revivify, a ranger would have no modifier, and a wizard or a fighter would have disadvantage.)
Before a 1st level cleric with a 16-17 WIS (+3) would have a 50/50 chance of casting a 4th level spell, so let's adjust the base DC for that. With advantage you have a 51% chance to roll a 15, so with Religion skill of +2 and INT of +0 that's 17. So the new DC should be 13 + spell level.
Now that 1st level cleric has the same chance (well, 1% more likely), how about a druid trained in Religion? Well, they need to roll a 15 or higher, so they have a 30% chance of casting that revivify scroll. Not bad for no chance before.
How about a fighter not trained in religion? 17 or higher with disadv turns into about a 4% chance to cast.
How about a wizard with a +3 INT mod trained in religion? Hmm, they need to roll 12 or higher, which is 20% of the time.
Let's look at the middle. +4 proficiency characters trying to read a 5th level scroll. (So base DC 18.)
Cleric can auto-read, since it's on his list and he can cast 5th level spells. (9th level is min for 5th.)
Say it's on the Paladin list. Trained gives +4, needs a 14 or higher with advantage. 58%
Ranger trained with religion has the same 14 or higher but without advantage is 35%.
Bard with religion expertise and +1 INT has +9 to the roll needs a 9, but with disadvantage. 36%. Very close to the ranger.
Barb with -1 INT and no training needs a 19 with disadvantage, leaving a minor 1% chance.
And now, the equivalent of a 3.5 UMD monster: The Cleric (Knowledge) 1 / Wizard 8 with Religion and Arcana expertise and INT +5 would need a lowly 5, and have two different spellcasting lists it could be on. If it's on either (remember, wiz 8 doesn't have 5th level spells) then advantage gives them a 96% chance of success. They will never have disadvantage (since they cast arcane and divine) so if it's not on either list they still have a 80% chance of casting a 5th level spell scroll. (And they cast in medium armor.)
So this does generally work, and it can be abused some which is more of a worry if spell scrolls are something that can be bought or otherwise obtained easily in your setting.