Demolitionist

Whereas most rogues hide and stealth across the battlefield, demolitionists arrive with a bang. They help their allies with booming and destructive explosives that, less so than giving them the tactical upperhand on the battlefield, simply blow it to bits. This doesn't mean they aren't strategic, they sow chaos and confusion with dauntless resolve as they dash away from their foes, leaving a niced explosive present for them behind.

Firecracker

Beginning when you choose this archetype at 3rd level, you gain proficiency with Alchemist's Supplies. In addition, all explosives you craft, find or simply use gain the siege propperty (they deal double damage to objects and structures).

Demolition Bombs

Also at 3rd level, you have learnt to craft special bombs for your roguish endeavors. You can craft any number of bombs when you finish a short or long rest, or as a bonus action on your turn. Either way, you can't create a number of bombs per long rest that exceeds twice your proficiency bonus. You can throw a bomb as an action, to a point you can see within 60 feet of you, or you can set it at a point you can touch by spending 1 minute placing it. If you do so, the bomb automatically explodes in 1 minute, 10 minutes or 1 hour (your choice). Some bombs require a saving throw, the DC= 8 + your proficiency bonus + your Dexterity modifier. 

Whenever you create a bomb, choose amongst one of these options:

• Fragmentation: When this bomb explodes, each creature in a 10 foot radius centred on it must succeed on a Dexterity saving throw or take piercing damage equal to your sneak attack damage dice + your Dexterity modifier.
• Flashbang: When this bomb explodes, each creature in a 10 foot radius centred on it must succeed on a Constitution saving throw or be blinded until the end of your next turn.
• Smoke: When this bomb explodes, a 15 foot radius sphere of smoke appears and lasts for a number of rounds equal to your proficiency bonus. The smoke makes the area heavily obscured for all creatures.

Explosive Improvisation

Starting at 9th level, you gain the following benefits:

• Parting Gift: Whenever a creature hits you with a melee attack or moves within 5 feet of you, you can use your reaction and throw one of your already armed bombs. As part of that reaction, you move out of the range of the bomb and its effect, and the bomb immediately explodes. The creature makes the saving throw, if any, at disadvantage.
• Remote Trigger: You can trigger a placed bomb to explode at any point, as long as you are within 240 feet of it.

Pyrotechnic Surprise

At 13th level, you have mastered the techniques to conceal and trigger explosions to exploit your foes' weaknesses. Creatures have disadvantage on saving throws against your bombs if they are surprised or can't see the bomb.

Additionally, whenever you are reduced to 0 hit points, you may cause all the bombs in your person to immediately detonate and explode. All damage you take this way causes you to fail only one death saving throw.

Finally, at the end of a short rest, you can create one bomb, regardless of how many bombs you have created today.

Master Demolitionist

By the time you've reached 17th level, your mastery over explosives is unparalleled. All damage from your bombs is increased by an amount equal to half your level. Alternatively, if the bomb deals no damage, the saving throw DC or its duration (your choice) is increased by an amount equal to your Dexterity modifier.

Additionally, whenever you roll initiative and you have no bombs available, whether on you or you have created all of them, you can immediately create one; and your capability to create bombs now restores itself on a short rest instead of a long rest.