Archer + Subterfuge + Tempest
Tempest allows for more roving and control of the battlefield, instead of Assassin’s Stealth build. For this, you won’t require Stealth as much nor will it be your main source of damage output. It still grants the 50% DMG bonus as well as letting you get out of fights, as an upgraded Ice Flask draws aggro. (Though you won’t be using this as much as the other two, Fire Flask and Lightning Flask.)
In the Tempest Skill Tree, you want all of the Flasks and these Passives in particular: Killer’s Alchemy and Ride the Storm. Fury of the Storm grants 10% DMG Bonus once your Stamina is lowered which won’t be happening often, considering Fire Flask removes cooldown for all abilities, while Flaskmaster is better as a general ability, as opposed to being directly related to Tempest’s success. Flaskmaster gives you +1 to Potions and grants 25% of not activating them when used. As an Archer, this makes for a very useful DPS tool as it can increase your output or, with Stealth, you can use Beeeeees with no disruption on the battlefield.
Flask of Ice does not need to be upgraded.
Ride the Storm is also useful, as it increases the duration of all Elixirs. With Fire Flask, you then get 8 seconds of Zero Cooldown Abilities. The difference is casting approximately 2 Long Shot (without Ride the Storm) and 3/4 Long Shot(with Ride the Storm), as animation speed is roughly two seconds.
In Subterfuge, in addition to Stealth, get Sleep and Mercy Killing. This is because, once using Lightning Flask you can run around the battlefield with little to no interruption. It works like Haste, so you’ll be able to race over to enemies and cast Sleep, followed up by attacking with general attacks until Fire Flask and Long Shot/Full Draw are available. Alternatively, you can cast Sleep on one enemy, while attacking the other, which will give your allies reprieve.
A good tactic is: Lighntning Flask + Sleep on your target. This will reduce your Stamina. Fire Flask + Full Draw, as this will get the benefit from Tempest’s Passive Fury of the Storm (10%), Archer’s Passive First Blood (15%) and the Full Draw’s 800% DMG on full health as well as the Auto-Crit from Mercy Killing. In addition, an upgraded Full Draw will knockout the opponent, putting them in the same state as Sleep. You could use Full Draw again, as it has no cooldown, to finish off the opponent and get another Auto-Crit from your Mercy Killing Passive.