If you already know what 35hp is, then you can skip this first section.
What is 35hp?
35hp is a "gamemode" popular in Counter-Strike games where players are restricted to melee and must knife the enemy players before they get knifed themselves. Players are reduced to 35 HP, making a single hit from an enemy fatal. Knifing will make you vulnerable for a few seconds, as you cannot knife during a cooldown period. Here is the only good video that I could find to describe 35hp:
Essentially, it’s a gamemode about how you move and when to attack, including heavy use of teamwork and strategy. Players need to account for where their enemies are, how to counter their attacks, what to do and when. Players make use of bunnyhopping, ladders, and basically every gameplay element in an effort to get the first strike.
Why for SDNL?
As a mutator for SDNL, this can make the gameworld more interesting for some people. This mutator would change the way the game would be played, and also let players make use of their melee weapons. If there is an achievement for using melee weapons a large number of times, players may use this as the go-to mutator to earn it.
Summary + Suggested Mechanics
This is a mutator that restricts players to melee weapons, and makes every weapon an instant kill. Melee weapons should have the same range, but if they don't, reduce the damage of the longer reaching weapons. Movement is encouraged to help you kill your enemies before they can kill you. Attacking will give you a few seconds of cooldown, so attack only when necessary or you will be left vulnerable. If respawning is a feature in SDNL, then obviously allow respawning.
Yeah, this is pretty dope. Always been a fan of melee-only modes in games. Chivalry comes to mind, but unless the devs or someone are willing to program such elaborate melee combat, this would be the next best thing.
If it does happen, I recommend adding two mutators to SDNL that are similar to each other: Instakill Melee, which is the 35hp gamemode with melee weapons you just described, and Instakill, which is just like that but with a railgun-esque weapon.