Tentative code for the Status Hazard meta https://www.smogon.com/forums/threads/status-hazard.3571986/

formats.js

'use strict';

exports.Formats = [
  //...
  {
    name: "[Gen 7] Status Hazard",
    desc: [
      `Status moves in a Pokemon's first and second move slots can become hazard-setting moves.`,
      `&bullet; <a href="https://www.smogon.com/forums/threads/status-hazard.3571986/">Status Hazard</a>`,
    ],
    mod: 'statushazard',
    ruleset: ['[Gen 7] OU'],
    restrictedMoves: [
      'Block', 'Mean Look', 'Spider Web',
      'Roar', 'Whirlwind',
      'Taunt',
    ],
    maxHazards: 2,
    onStart: function() {
      this.add('-message', "Remember, status moves in your first two move slots can become status hazards!");
      let maxHazards = this.getFormat().maxHazards;
      if (maxHazards) {
        this.add('-message', `Only ${maxHazards} may be set at once per side.`);
      }
    },
    onModifyMovePriority: -999,
    onModifyMove: function(move, pokemon, target) {
      if (move.category === 'Status' 
          && ["normal","allAdjacentFoes","allAdjacent","adjacentFoe"].includes(move.target) 
          && pokemon.moves.indexOf(move.id) < 2
          && !this.getFormat().restrictedMoves.map(toId).includes(move.id)) 
      {
        move.statusHazard = true;
        move.target = "foeSide";
        move.flags['reflectable'] = true;
        //anything else?
      }
    },
    onTryHitSidePriority: -999,
    onTryHitSide: function(target, source, move) {
      if (move.statusHazard) {
        target.side.addSideCondition('statushazard');
            
        let s = target.side.sideConditions['statushazard'];
            
        let currentHazards = s.hazards.map(a => a.id);
        if (currentHazards.includes(move.id)) return false;
        
        //accuracy check time!
        let boostTable = [1, 4 / 3, 5 / 3, 2, 7 / 3, 8 / 3, 3];
        let accuracy = move.accuracy;
        let boosts, boost;
        if (accuracy !== true) {
          if (!move.ignoreAccuracy) {
            boosts = this.runEvent('ModifyBoost', source, null, null, Object.assign({}, source.boosts));
            boost = this.clampIntRange(boosts['accuracy'], -6, 6);
            if (boost > 0) {
              accuracy *= boostTable[boost];
            } else {
              accuracy /= boostTable[-boost];
            }
          }
        }
        //run accuracy modifiers! but we don't have a target...
        //The hack is to run the ModifyAccuracy event with no target (global modifiers like Gravity)
        //and then pretend SourceModifyAccuracy is an event in its own right (source modifiers like CompoundEyes).
        //There are many ways this could go wrong, like if the user's ally had an onAllyModifyAccuracy,
        //or if a foe sideCondition had a ModifyAccuracy. We would want to account for both of these.
        //Thankfully, I don't believe these cases exist.
        accuracy = this.runEvent('ModifyAccuracy', null, null, move, accuracy);
        accuracy = this.runEvent('SourceModifyAccuracy', source, null, move, accuracy);
        if (move.alwaysHit || source.hasAbility('noguard') || (move.id === 'toxic' && source.hasType('Poison'))) {
          accuracy = true;
        } else {
          //i dont think either of these do anything
          accuracy = this.runEvent('Accuracy', null, null, move, accuracy);
          accuracy = this.runEvent('SourceAccuracy', source, null, move, accuracy);
        }
        
        if (accuracy !== true && this.random(100) >= accuracy) {
          this.add('-miss', source, target);
          return false;
        }
        
        //---hit line---
        move.target = 'normal';
        if (move.selfdestruct === 'ifHit') { //Memento case
          this.faint(source);
          delete move.selfdestruct;
        }
        if (move.selfSwitch) { //Parting Shot case
          source.switchFlag = move.fullname;
          delete move.selfSwitch;
        }
        if (['defog', 'curse'].includes(move.id)) { //super-special cases
          this.singleEvent('Hit', move, null, target, source, move);
          delete move.onHit;
        }
        
        let maxHazards = this.getFormat().maxHazards;
        if (maxHazards && s.hazards.length === maxHazards) {
          let removedHazard = s.hazards.shift();
          s.sources.shift();
          this.add('-message', `The ${removedHazard.name} hazard vanished!`);
          this.add('-sideend', target.side, `hazard:${removedHazard.id}`, '[silent]');
        }
            
        this.add('-message', `A ${move.name} hazard was set!`);
        this.add('-sidestart', target.side, `hazard:${move.id}`, '[silent]');
        s.hazards.push(move);
        s.sources.push(source);
        
        return null;
      }
    },
  },
  //...
};

moves.js

'use strict';

exports.BattleMovedex = {
  'defog': {
    inherit: true,
    boosts: {evasion: -1},
    onHit: function (target, source, move) {
      let removeTarget = ['reflect', 'lightscreen', 'auroraveil', 'safeguard', 'mist', 'spikes', 'toxicspikes', 'stealthrock', 'stickyweb'];
      let removeAll = ['spikes', 'toxicspikes', 'stealthrock', 'stickyweb'];
      for (let targetCondition of removeTarget) {
        if (target.side.removeSideCondition(targetCondition)) {
        if (!removeAll.includes(targetCondition)) continue;
          this.add('-sideend', target.side, this.getEffect(targetCondition).name, '[from] move: Defog', '[of] ' + target);
        }
      }
      for (let sideCondition of removeAll) {
        if (source.side.removeSideCondition(sideCondition)) {
          this.add('-sideend', source.side, this.getEffect(sideCondition).name, '[from] move: Defog', '[of] ' + source);
        }
      }
      target.side.removeSideCondition('statushazard');
      source.side.removeSideCondition('statushazard');
    },
  },
  'rapidspin': {
    inherit: true,
    self: {
      onHit: function (pokemon) {
        if (pokemon.hp && pokemon.removeVolatile('leechseed')) {
          this.add('-end', pokemon, 'Leech Seed', '[from] move: Rapid Spin', '[of] ' + pokemon);
        }
        let sideConditions = ['spikes', 'toxicspikes', 'stealthrock', 'stickyweb'];
        for (const condition of sideConditions) {
          if (pokemon.hp && pokemon.side.removeSideCondition(condition)) {
            this.add('-sideend', pokemon.side, this.getEffect(condition).name, '[from] move: Rapid Spin', '[of] ' + pokemon);
          }
        }
        if (pokemon.hp && pokemon.volatiles['partiallytrapped']) {
          pokemon.removeVolatile('partiallytrapped');
        }
        if (pokemon.hp) pokemon.side.removeSideCondition('statushazard');
      },
    },
  },
};

statuses.js

'use strict';

exports.BattleStatuses = {
  'statushazard': {
    onStart: function(side, source, sourceEffect) {
      this.effectData.hazards = [];
      this.effectData.sources = [];
    },
    onSwitchInPriority: -999, //run after other SwitchIn events
    onSwitchIn: function(pokemon) {
      for (let i = this.effectData.hazards.length - 1; i >= 0; i--) {
        //Status hazards take effect in order from newest to oldest.
        let hazard = this.effectData.hazards[i];
        let removed = [];
        if (hazard.status && !this.getImmunity(hazard.status, pokemon) && !pokemon.hasType('Steel')) {
          //Remember, we only remove hazards if the type of the target is naturally immune to a major status, Steel types excepted.
          this.add('-message', `The ${hazard.name} hazard vanished!`);
          this.add('-sideend', `hazard:${hazard.id}`, '[silent]');
          removed.push(i);
        } else {
          this.add('-message', `The Pokemon was affected by the ${hazard.name} hazard!`);
          this.moveHit(pokemon, this.effectData.sources[i], hazard); //i doubt we need isSelf or isSecondary flags
        }
        this.effectData.hazards = this.effectData.hazards.filter((v, i) => !removed.includes(i));
        this.effectData.sources = this.effectData.hazards.filter((v, i) => !removed.includes(i));
      }
    },
    onEnd: function(side) {
      this.add('-message', 'The status hazards vanished from the battlefield!');
      for (let hazard of this.effectData.hazards) {
        this.add('-sideend', side, `hazard:${hazard.id}`, '[silent]');
      }
    },
  },
};

The alpha release of Status Hazard is finished as of March 4. This code is untested, therefore there are no known bugs yet. Some bugs I predict will happen, however:

• Moves that call another move (Metronome, Assist, etc) will not have their moves upgraded to Status Hazards even if they are eligible
• Misc. weird behavior when the Pokemon that set a hazard is not active when the hazard triggers

Wow, Status Hazard is suddenly playable on R.O.M.! I do not know how long it has been there, but I was alerted to this last week.

Actually, this worries me a bit. I have neither changed nor tested the code since early March, and nobody has given me feedback, either. If my code had errors, I would have liked to know about them so that either 1. I could try to fix them myself, or 2. someone else could fix them and I could learn from them. Because I can't find the server source for ROM, I have no way of telling if my code or someone else's was used.