My expectation is that I'm able to buy almost infinite supply of common scrolls and at least 10 of each uncommon scrolls every time I roll back to town after a quest. Obviously 2-3 rare scrolls of each spell would also be available to me for purchase. Isn't that the case? That's how it was in 3.5e...

@PentaKon That is not the default case, it is entirely within the arena of the DM's worldbuilding. If that is what your DM permits, then UMD will have a lot of flexibility for you, but the bottom line is that UMD is really only as good as the DM allows it to be.

@PentaKon In my experience the thief subclass is just fine, even without being able to make extensive use of UMD. I played Tier 4 game that ran for ten sessions or so as a thief rogue, and didnt use UMD once, and I didnt feel like I was missing anything.

We usually have munchkin characters. I'm investigating how to migrate my 3.5e shadow pouncer rogue with 21 sneak attacks per round to 5e. Without overpowered UMD the Thief's toolkit seems massively underwhelming compared to the ATrickster.

@PentaKon Any DM who allows you that is making a mistake. I'm investigating how to migrate my 3.5e shadow pouncer rogue with 21 sneak attacks per round to 5e. Without overpowered UMD the Thief's toolkit seems massively underwhelming compared to the ATrickster The power curves for 3.5 and 5 are different. Strongly suggest that you treat 5e as a new game, and discard previous edition assumptions. (I had to do that to start enjoying it). Strongly suggest that you look up bounded accuracy

No, I'm fine with the way 5E is (i've already played half of Avernus with my Wizard). The issue is that if we migrate an existing campaign to 5E we're going to be forced to create characters that closely resemble our 3.5E chars both in RP and in combat builds. Obviously my DM has shutdown my 21 sneak attack build and has made my character which I invested 15 levels to make possible completely useless by providing all serious enemies with SA immunity and teleportation blocking (which is what enables a shadow pouncer to do lots of attacks) so essentially my rogue in 3.5E is 100% useless :)

@PentaKon The issue is that if we migrate an existing campaign to 5E we're going to be forced to create characters that closely resemble our 3.5E chars both in RP and in combat builds I have no idea what's forcing you, but as I don't get to play in that campaign, I'll just say best wishes and I hope you have fun with it. I think we have some Q&A here about migrating PCs from one edition to another. My suggestion is: don't bother. Just make a similar one at a similar level from within the system. (Feats are a way to customize that, however; maybe a question on feats would help you?

@KorvinStarmast the DM will probably force us. We are level 18 (started at lvl 6) and we're playing a custom story which is supposedly built around our choices. Our Wizard isn't just a Wizard but a Fatespinner-Archmage, known for defying fate etc. The Cleric is a follower of Ilmater that is trying to find a safe place for his persecuted covenant. As you said we'll have to make similar characters, as similar as possible. Like, the Wizard will have to be a Diviner and such. Since my Rogue is a Shadowlord and spams UMD as well I was split between the Thief and Arcane Trickster.

@PentaKon Have you looked into the phantom rogue?

@ThomasMarkov Just found out today there are other archetypes apart from the PHB ones! I'll take a look at them as well although along with Eberron our campaign has banned anything Psychic so one of them is off :)

Nice answer! It's also worth noting (since scrolls got specifically mentioned) that a Thief with UMD will get a lot less "bang for their buck" out of Spell Scrolls than a 13th level character that actually has those spells on their list. At best, the Thief will have a 50% chance of successfully using the scroll, usually less.

@Gandalfmeansme not really, I think with the Rogue ability Reliable Talent where all ability check d20 rolls have a minimum value of 10, you almost guaranteed success on scrolls of 5th level and below