/*
 * This file is part of Sponge, licensed under the MIT License (MIT).
 *
 * Copyright (c) SpongePowered <https://www.spongepowered.org>
 * Copyright (c) contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.spongepowered.test;

import org.spongepowered.api.Sponge;
import org.spongepowered.api.command.CommandResult;
import org.spongepowered.api.command.spec.CommandSpec;
import org.spongepowered.api.entity.living.player.Player;
import org.spongepowered.api.event.Listener;
import org.spongepowered.api.event.entity.DestructEntityEvent;
import org.spongepowered.api.event.filter.Getter;
import org.spongepowered.api.event.game.state.GameInitializationEvent;
import org.spongepowered.api.plugin.Plugin;

@Plugin(authors = "gabizou", name = "DeathTest", id = "deathtest", description = DeathTest.DESCRIPTION, version = "0.0.0")
public class DeathTest {

    public static final String DESCRIPTION = "Use /toggleDeath to toggle whether players can die";
    private boolean allowDeathsOfPlayers = true;

    @Listener
    public void onInit(GameInitializationEvent event) {
        Sponge.getCommandManager().register(this, CommandSpec.builder()
            .executor((src, args) -> {
                this.allowDeathsOfPlayers = !this.allowDeathsOfPlayers;
                return CommandResult.success();
            }
            )
            .build(), "toggleDeath");
    }

    @Listener
    public void onDeath(DestructEntityEvent.Death entityEvent, @Getter("getTargetEntity") Player player) {
        if (!this.allowDeathsOfPlayers) {
            entityEvent.setCancelled(true);
        }
    }

}

/*
 * This file is part of Sponge, licensed under the MIT License (MIT).
 *
 * Copyright (c) SpongePowered <https://www.spongepowered.org>
 * Copyright (c) contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.spongepowered.test;

import org.spongepowered.api.Sponge;
import org.spongepowered.api.command.CommandResult;
import org.spongepowered.api.command.spec.CommandSpec;
import org.spongepowered.api.entity.living.player.Player;
import org.spongepowered.api.event.Listener;
import org.spongepowered.api.event.entity.DestructEntityEvent;
import org.spongepowered.api.event.filter.Getter;
import org.spongepowered.api.event.game.state.GameInitializationEvent;
import org.spongepowered.api.plugin.Plugin;

@Plugin(authors = "gabizou", name = "DeathTest", id = "deathtest", description = DeathTest.DESCRIPTION, version = "0.0.0")
public class DeathTest {

    public static final String DESCRIPTION = "Use /toggleDeath to toggle whether players can die";
    private boolean allowDeathsOfPlayers = true;

    @Listener
    public void onInit(GameInitializationEvent event) {
        Sponge.getCommandManager().register(this, CommandSpec.builder()
            .executor((src, args) -> {
                this.allowDeathsOfPlayers = !this.allowDeathsOfPlayers;
                return CommandResult.success();
            }
            )
            .build(), "toggledeath");
    }

    @Listener
    public void onDeath(DestructEntityEvent.Death entityEvent, @Getter("getTargetEntity") Player player) {
        if (!this.allowDeathsOfPlayers) {
            entityEvent.setCancelled(true);
        }
    }

}

Change 'toggleDeath' command alias to 'toggledeath'