[Psyk0tik]

Untested.

PHP Code:

#include <sourcemod>
#include <tf2>
#include <adminmenu>

#pragma semicolon 1
#pragma newdecls required

#define ASC_VERSION "1.0"

public Plugin myinfo =
{
    name = "[TF2] Air Swim Condition",
    author = "ApoziX and Psyk0tik (Crasher_3637)",
    description = "Provides a command to toggle air swim condition on players.",
    version = ASC_VERSION,
    url = "https://forums.alliedmods.net/showthread.php?t=311471"
};

public APLRes AskPluginLoad2(Handle myself, bool late, char[] error, int err_max)
{
    if (GetEngineVersion() != Engine_TF2)
    {
        strcopy(error, err_max, "This plugin only supports Team Fortress 2.");
        return APLRes_SilentFailure;
    }

    return APLRes_Success;
}

bool g_bAirSwim[MAXPLAYERS + 1];

public void OnPluginStart()
{
    LoadTranslations("common.phrases");
    RegAdminCmd("sm_swim", cmdAirSwim, ADMFLAG_GENERIC, "Toggle air swim condition for players.");
    CreateConVar("asc_version", ASC_VERSION, "Plugin version", FCVAR_NOTIFY|FCVAR_DONTRECORD);
}

public void OnClientPutInServer(int client)
{
    g_bAirSwim[client] = false;
}

public Action cmdAirSwim(int client, int args)
{
    if (!bIsValidClient(client))
    {
        ReplyToCommand(client, "[SM] You must be in-game to use this command.");
        return Plugin_Handled;
    }

    char target[32], target_name[32], toggle[32];
    int target_list[MAXPLAYERS], target_count;
    bool tn_is_ml;
    GetCmdArg(1, target, sizeof(target));
    GetCmdArg(2, toggle, sizeof(toggle));
    int toggler = StringToInt(toggle);

    if (args != 2 || toggler < 0 || toggler > 1)
    {
        if (IsVoteInProgress())
        {
            ReplyToCommand(client, "[SM] Usage: sm_swim <#userid|name> <0|1>");
        }
        else
        {
            vMenuSwim(client, 0);
        }

        return Plugin_Handled;
    }

    if ((target_count = ProcessTargetString(target, client, target_list, MAXPLAYERS, COMMAND_FILTER_ALIVE, target_name, sizeof(target_name), tn_is_ml)) <= 0)
    {
        ReplyToTargetError(client, target_count);
        return Plugin_Handled;
    }

    for (int i = 0; i < target_count; i++)
    {
        if (bIsValidClient(target_list[i]))
        {
            switch (toggler)
            {
                case 0:
                {
                    TF2_RemoveCondition(target_list[i], TFCond_SwimmingCurse);
                    PrintToChat(target_list[i], "[SM] You cannot air swim anymore.");
                }
                case 1:
                {
                    TF2_AddCondition(target_list[i], TFCond_SwimmingCurse, TFCondDuration_Infinite);
                    PrintToChat(target_list[i], "[SM] You can now air swim.");
                }
            }
        }
    }

    if (tn_is_ml)
    {
        ShowActivity2(client, "[SM] ", "Toggled air swimming for %t.", client, target_name);
    }
    else
    {
        ShowActivity2(client, "[SM] ", "Toggled air swimming for %s.", client, target_name);
    }

    return Plugin_Handled;
}

void vMenuSwim(int client, int item)
{
    Menu mSwimMenu = new Menu(iSwimMenuHandler);
    mSwimMenu.SetTitle("Choose a player:");
    AddTargetsToMenu(mSwimMenu, client, true, true);
    mSwimMenu.DisplayAt(client, item, MENU_TIME_FOREVER);
}

public int iSwimMenuHandler(Menu menu, MenuAction action, int param1, int param2)
{
    switch (action)
    {
        case MenuAction_End: delete menu;
        case MenuAction_Select:
        {
            char sInfo[32];
            menu.GetItem(param2, sInfo, sizeof(sInfo));
            int iTarget = GetClientOfUserId(StringToInt(sInfo));

            if (iTarget == 0)
            {
                PrintToChat(param1, "[SM] %t", "Player no longer available");
            }
            else if (!CanUserTarget(param1, iTarget))
            {
                PrintToChat(param1, "[SM] %t", "Unable to target");
            }
            else if (!IsPlayerAlive(iTarget))
            {
                PrintToChat(param1, "[SM] %t", "Player has since died");
            }
            else
            {
                switch (g_bAirSwim[iTarget])
                {
                    case true:
                    {
                        TF2_RemoveCondition(iTarget, TFCond_SwimmingCurse);
                        g_bAirSwim[iTarget] = false;
                        PrintToChat(iTarget, "[SM] You cannot air swim anymore.");
                    }
                    case false:
                    {
                        TF2_AddCondition(iTarget, TFCond_SwimmingCurse, TFCondDuration_Infinite);
                        g_bAirSwim[iTarget] = true;
                        PrintToChat(iTarget, "[SM] You can now air swim.");
                    }
                }

                ShowActivity2(param1, "[SM] ", "Toggled air swimming for %N.", iTarget);

                if (IsClientInGame(param1) && !IsClientInKickQueue(param1))
                {
                    vMenuSwim(param1, menu.Selection);
                }
            }
        }
    }

    return 0;
}

stock bool bIsValidClient(int client)
{
    if (client <= 0 || client > MaxClients || !IsClientInGame(client))
    {
        return false;
    }

    return true;
}