I wanted to ask about allowing the Rogue sub-class (Assassin) to benefit from Supreme Sneak.
I have a player in my campaign who plays as an Assassin Rogue and would like to have access to the Supreme Sneak upgrade at level 9, which normally is part of the Thief build.
Her argument is that Supreme Sneak is more appropriate to an Assassin because of its synergy with Assassinate. I can see her point and I don't have any problems with allowing this, but I wanted to know if there are any glaring problems with doing this.
Would allowing a Rogue (Assassin) to benefit from Supreme Attack upon reaching level 9, instead of the regular Infiltrator Expertise, make the sub-class very unbalanced?
Here are descriptions of the relevant class features:
Assassinate (Assassin)
Starting at 3rd level, you are at your deadliest when you get the drop on your enemies. You have advantage on attack rolls against any creature that hasn’t taken a turn in the combat yet. In addition, any hit you score against a creature that is surprised is a critical hit.
Supreme Sneak (Thief)
Starting at 9th level, you have advantage on a Dexterity (Stealth) check if you move no more than half your speed on the same turn.
Infiltrator Expertise (Assassin)
Starting at 9th level, you can unfailingly create false identities for yourself. You must spend seven days and 25 gp to establish the history, profession, and affiliations for an identity
(PHB p.97)
Best Answer
I think this change would be fine
A common complaint about the Assassin roguish archetype is that its level 9 and 13 features are quite lackluster. They only make sense in specific scenarios, which may not come up in your campaign, making them completely useless. I agree with your player that Supreme Sneak does suit the Assassin from a flavour perspective, and if it helps that player to feel like their choice at level 3 wasn't a mistake, I don't see a problem with it.
Mechanically, it is a straight up trade. They aren't gaining Supreme Sneak in addition to Infiltrator Expertise, it's instead of. It also doesn't have any multiclassing issues, such as giving a feature from a different class to this character; any character would need 9 levels in rogue either way. This isn't a particularly strong feature, like the features that roguish archetypes gain at level 3; their level 9 feature is usually somewhat of a ribbon feature. Rogues generally are also considered to have a strong "core class", so they don't gain that much additional power from their archetype features.
I also don't see there being a balance issue in combining Assassinate with Supreme Sneak. Although I agree with your player that Supreme Sneak suits an assassin, I don't think it leads to any game-breaking combinations, since an Assassin rogue is very likely already extremely sneaky (proficiency and likely Expertise in Stealth; credit to Cubic for pointing this out first, but I wanted to back up my answer with this point also).
The only thing I would add is that it might be worth making sure your other players are alright with this change, especially since I imagine your Assassin player is the only one who will be getting this change. It shouldn't become a free-for-all where people can basically just mix-and-match their favourite features from all of their class's archetypes. Assassin is somewhat of a special case because of how weak their level 9 and 13 features are considered to be, given that they are very campaign-specific.