Fight For Your Freedom. Guerrilla Fighting Style.

Art By: QuintusCassius

Link: 

https://www.deviantart.com/quintuscassius/art/Ambush-743748360

Guerrilla Fighting Style (Requires: Ranger or Paladin)

At the start of your first turn of each combat, you can make one ranged or melee attack with advantage. If that attack hits you can add your proficiency bonus to the damage roll.

Balancing Notes

Guerrilla Fighting by design is intended to give a character a reliable first round punch that falls off after the first round of combat. 

I've decided against giving this fighting style to Fighters because they get their fighting style at 1st level instead of 2nd level. The reason for this decision is the nasty synergy of first round Advantage and Sneak Attack this fighting style gives Rogues.

The synergetic boost of power that is first round Advantage and Sneak Attacks is perfectly fine within balance tolerances of 5e DnD and it is not my intention to make such a synergy impossible. At the same time, however I think its reasonable to want this synergy to be about as difficult to get as a 3rd level Assassin Rogue dip while working within the frame work of DnD 5e. With that said, if feel free to do whatever you want. It's your game after-all all.

In my internal play test, I found that things like adding a 1d6 or 1d8 die to your first round of attack added a bit too much early game power beyond the "~1-ish extra damage per attack" value for a Fighting Style and would fall off at the very late game. I also noted that any attempt to try to make this fighting style scale at certain levels with larger dice tended to make the wording more complicated then desired. Thus in the end, I decided to have the extra damage scale intuitively by using a players proficiency bonus.

This also made balancing easier as fighting styles tend to be worth "~1-ish extra damage per attack" or half a feat. For an example, at levels 2-4 a Character who gets off an an ambush with this Guerrilla Fighting will have about a 4 damage advantage over a Character with another fighting style in a combat. Thus it will take another fighting style about Four turns to catch up to Guerrilla Fighting or the equivalent of a longish combat. On the other hand if a Character doesn't get an ambush off he or she will only have a two turn advantage, the equivalent of a short combat before they would be better off with another fighting style.

In short, Guerrilla Fighting is meant to be especially strong in short skirmishes and hit and fade ambushes, but yet falls off quickly if a battle devolves into a drawn out slugging match when compared to offical Fighting Styles in the PHB.