Cloaks and daggers can only go so far in a world that people can manipulate realty with song and dance or become so angry that they ignore death. Luckily for you there are more logical and easy solutions to your problems.
Level 3
Quick Learner.
You craft potions and poisons for half the cost and time.
The Hidden Stash.
Whenever you Safe Rest roll INT d6 and gain the corresponding potions or poisons from the concoctions table. They last until your next Safe Rest.
Level 7
Intoxicating Strike.
Whenever you sneak attack you may apply one poison as part of the attack action. (The poison takes effect on the same attack.) Additionally you now roll d8s when rolling on the concoctions table and roll INT + 1 time
That's where I left 'ya!.
(1/encounter) Duplicate the last poison or potion you used. It lasts until your next Safe Rest.
Level 11
An Eye for the Good Stuff.
Immediately learn the effects of a potion you see. Additionally you now roll d10s on the concoctions table and roll INT + 2 times
Down the Drain.
(1/round) Administer or drink a potion for free.
Level 15
The Flow State.
If you are under the effect of 5 or more different potions you may set one of the dice of Sneak Attack to whatever you like. Additionally you now roll d12s on the concoctions table and roll INT + 3 times
Concoctions
Unless specified effects last until the end of the affected creature's next turn. Poisons affect the weapon until the encounter ends. When administered to another creature the potions apply your INT score.
1. Corpse Reviver #3.
Regain INT d6+6 HP.
2. Martini Express.
Gain INT speed until the encounter ends.
3. Old Fashioned Fortitude.
Gain INT armor until the encounter ends.
4. Pain on the Beach.
Poison: On hit deal INT bonus damage.
5. Killerpain.
Poison: On hit next attack against the creature is made with advantage.
6. Dark 'n' Storming Mad.
Poison: On hit the creature is taunted by you.
7. Pina- Cola-boration.
Gain (1/round) help for free
8. Moscow Mule's Weigh.
Poison: On hit the creature is slowed.
9. Bloodhound's Mary.
Gain (1/round) ignore the penalty for rushed attacks.
10. Drain-quiri.
Poison: On hit gain INT temp HP.
11. Clarity Collins.
Gain Advantage on attack rolls until the encounter ends.
12. Bile Sour.
Poison: On hit creature is poisoned until end of their next turn.