https://fights-in-tight-spaces.fandom.com/wiki/Grapple
This card re-positions the enemy adjacent to you, but it also faces them away from you. Even if the enemy has auto-attack, the enemy won't be able to face you nor will they auto-attack you unless you move or play a card that has movement. See also: https://fights-in-tight-spaces.fandom.com/wiki/Redirect

https://fights-in-tight-spaces.fandom.com/wiki/Throw
Throw is a very basic card that allows you to knock down a target and stun them next turn. It doesn't work on all enemies, but it does work on most. There are other cards in the same vein, and I personally like Suplex which can re-position the enemy similar to Grapple.

https://fights-in-tight-spaces.fandom.com/wiki/Pocket_Sand
Pocket Sand stuns an enemy for a turn, preventing them from taking any actions until next turn. While short on duration, this card ignores block which many other stuns do not. Counter Stun, which is a defensive card, works similar to Pocket Sand, except it triggers when you take damage from 1 to 2 tiles away, stunning the enemy regardless of armor.

There are three primary strategies for dealing with the dreaded mohawk man (rifle boss), which I will go into shortly, but first lets discuss how you can mitigate damage and approach the rifle boss.

First off, do not be afraid to take a hit from his rifle, especially early on when it only does 10 damage, if you have a sure way to kick his ass. If your deck contains block cards, one is usually enough to get close to him via a movement card. You can also approach him from the side, where he will turn to face you if you are adjacent but will not shoot you, right away at least.

If you approach him from the front though, you will always get shot, even if you Shift past an enemy or whatever else.

Now, the three primary takedown strategies:

1. Disable
This is a very reliable way to shut down what the rifle boss can do. You want knockdown cards, such as Throw, Suplex, Takedown, and so on. Anything that throws the target to the ground will work here. Once used, the rifle boss will be on the ground on your turn and then dizzy for the turn following, at which time he will be unable to do anything.

You can also use something like Pocket Sand to stun him for a turn to prevent him from acting, but he will act normally the turn following.

2. Ring-out
This assumes you can re-position the rifle boss to where you can knock him off/out a building/room. Actually not as hard as it may seem, but you need the Grapple card or some way to position him for a ringout. You can combine this strategy with the first one, disable, to stun the rifle boss in a position you want, and then ring him out the following turn. I think this is the safest strategy overall.

3. Knock-out
If you have a lot of hard-hitting, upgraded cards, approach the boss as described above, stun or re-position him so that he cannot attack you directly, use something like Steel Self to increase your damage, and then unload. Fairly easy when you first encounter this enemy, but not as reliable late-game.

1. Disable

2. Ring-out

3. Knock-out

Bonus Example, Starting on the Same Level

Hope that helps. Keep in mind that you can use other enemies to block line of sight or make the rifle boss shoot them, which he will happily do, so don't forget your movement. The rifle boss has a 2-tile movement range, so if you move 3 tiles, he won't be able to target you in most situations.