Help in getting a second sneak attack

[DEFCON 1]

Here's one possible solution

Panther Strike Bracers (requires attunement)
Panther strike bracers allow you to answer an unsuccessful melee attack against you with an unexpected riposte. Spend your reaction to make an opportunity attack immediately after an enemy
has missed you with a melee attack. If this opportunity attack also misses, the bracers can't be used
again until you take a short rest.

I modeled them after Counterstrike Bracers from d20.

That looks like it could be okay. They are kind of an adaptation of what you could do with the Martial Adept feat-- that one allows you to take Riposte (plus another maneuver) and use it once per short rest (while adding an extra d6 to damage from the superiority die). Your magic item instead removes the second maneuver and the extra damage, and instead allows for a rolling continuation of usage so long as you don't miss. So it could be once per short rest, it could be every round of combat per short rest depending on the player's luck. I don't see any major issues with it. If raising up the Rogue's damage is the true concern though... I might just give it a 3/charges per Short/Long Rest, rather than having it cease function on a miss. Three extra Sneak Attacks per fight won't be any major unbalancing factor compared to the rest of the party, and you avoid the issue of the Rogue missing with his first OA and then not getting to use the item again until they rest with not a single extra SA coming out of it.

Your other big issue will be whether any of your other players might try and take the item (like the Monk for example) because extra OAs are always welcome for almost any melee weapon users. You'll need to come up with a reason to get the item to the rogue or make sure your group gives it to him.

 

[Tales and Chronicles]

Another item (the last one, I promise)

Dagger of Follow-Trout
This dagger is a fine example of a potent item originating from miscommunication. The Shahuagin bard Merklos Keel-Bitter ordered a fine weapon which would complement elegantly his favored fighting style. However, because of the messaging spell he used being corrupted (or some would say that the mage-enchanter also had a bad sense of humor and an even worst understanding of Shahuagins comedy), the created weapon was made in the shape of a ungracious fish with a dumb look and branded as the Follow-Trout dagger instead of the more adequately named Follow-Through dagger. Still the error was rectified by another talented, yet humorless, Duergar smith who gave the dagger its potent magic properties when the first enchanter was found drown in a pond.

Weapon, Unique item, rogue only, require Attunement
- If a rogue hits a creature with an attack on its turn, he may use its reaction to make a single other attack at the end of the creature's turn.
- The user gain swim speed of 20.
- The user also smells like fish

 

[jgsugden]

Another suggestion to consider when a player has an underpowered PC - give them extra PC status.

For example, you can allow them to have an NPC animal that joins them in battle and complements their PC's capabilities. Or, you can give them a loyal squire/henchman/hireling that is a few levels lower than he rest of the party. Or you can have an NPC monster take a liking to them and accompany the PCs (under that player's control).

 

[CTurbo]

Random nameless Rogue Feat:

On your turn, when you score a critical hit or reduce a creature to 0 hit points, you can make another Attack with the same weapon against a different creature that is within 5 feet of the original target and within range of your weapon. You can apply your sneak attack damage to the second target.

Before you make a melee attack with a light or finesse weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add 3d6 to the attack's damage.


Obviously modeled after GWM with a touch of Horde Breaker. The first feature is stronger, but even more conditional. The second feature is more of a gamble. I could see changing it to 2d6