My party is currently level 6, and consists of a Halfling Rogue, Human Druid, Halfling Barbarian, and Half-Elf Monk. They're all excellent players who play tactically and know their class well. I'm currently running into a problem with the Rogue and the Druid.
My Rogue has Expertise in Stealth (+10 at this level) and a Cloak of Elvenkind. This means that her minimum roll (barring four 1s because they're a Halfling) on a Stealth check is a 12, and her average roll is around a 25. Even on a minimum roll, most NPCs will not be able to see her (and in a few levels that will extend to all NPCs).
However, the party's current methodology is to have the Druid do the sneaking instead of the Rogue. Their reasoning is that even though it's highly unlikely that the Rogue will get caught, if she does get caught then really bad things happen – the enemy will know they're being spied on, the Rogue gets captured, etc. However, the Druid is spying in the form of a rat, spider, owl, or other sneaky animal, so if a bandit spots a bat they probably won't think much of it. Additionally, the druid will have a much easier time escaping a secure location (say, by summoning 8 Giant Badgers and then Wild Shaping into a spider).
Here's my problem with this: I see "Being Sneaky" as a core part of a Rogue's class identity, and the player has invested a lot of resources (proficiency, expertise, and an attuned item) into being sneaky. I try to give all of my players a chance to live out their class identity: The Barbarian gets to hulk out and smash things, the Druid gets to save Dryads and heal cursed forests, the monk gets to take people down bare-handed, etc. I want to have at least some opportunities for the Rogue to get to experience this key feature of their class by sneaking into a secure location or scouting out an enemy party.
How can I design stealth-based encounters or challenges so that the Rogue will be a better choice than the Druid?
Best Answer
Encouraging them to have the rogue be sneaky doesn't necessarily require discouraging them from using the druid. Where possible, encourage them to work together. The druid can scout ahead to give the rogue information about the layout and the guards, create distractions, or keep watch while the rogue picks locks, dispatches guards, and the like. Each can handle the aspects of the challenge better suited to them, or give bonuses to their compatriot.
This has more players involved and opens up more interesting strategies.
The Vlad Taltos novels offer some good ideas. Vlad is an assassin (at least initially) but also a witch (Gender neutral term in the setting) with a familiar (Loiosh) who is essentially a tiny wyvern with an ecological niche very roughly in the vicinity of raven/raccoon/vulture/rat and they are telepathically linked. Loiosh is sometimes a distraction, often a scout, and always sarcastic.
Heist movies (Ocean's Eleven, etc) also give some good ideas for how to run co-op sneak this, as well as maybe some ways other part members could get in on it.
If you were running GURPS I would recommend making heavy use of Complementary Skills (Make a skill roll which then based on success gives a small modifier to another skill, possibly made by another player) For instance one player rolls Fast-Talk to distract a guard which gives a bonus (Or penalty on crit failure) to another player using Stealth. I'm not sure how adaptable this would be to D&D though.