Ages ago in the minor suggestions thread I suggested creative blocks that act as sensors. Now I reiterate that suggestion with a few changes.
Creative Sensor Blocks
Sensor Blocks would only be available and configurable to those in creative mode.
Sensor blocks, when a creature passes in front of them, emit a redstone signal.
They would provide interesting ways for adventure map makers to trigger command blocks and other types of traps. Possible even be used as makeshift wireless redstone
Right Clicking the block will bring up a GUI that allows you to adjust the range of the sensor and what creatures it targets.
Sensitivity: The sensitivity can can be adjusted from 0 to possibly 32 squares.
Valid Targets: A semi colon delimited list can be used to specify what entity ids the command block can sense
'HostileMob' is short for 'Blaze;CaveSpider;Creeper;EnderDragon;Ghast;Giant;LavaSlime;Silverfish;Skeleton;Slime;Spider;Witch;WitherBoss;Zombie'
'NeutralMob' is short for 'Enderman;PigZombie;Villager;IronGolem'
'Animal' is short for 'Bat;Chicken;Cow;Ozelot;Pig;Squid;Wolf'
'Player' would detect players.
'Projectile' is short for 'Arrow;Snowball;Egg;Fireball;SmallFireball;ThrownEnderpearl;ThrownExpBottle;ThrownPotion;WitherSkull'
It could also detect things like Boats, Minecarts, Dropped Items, XP Orbs, Primed TNT, even falling dynamic tiles like sand, gravel, dragon eggs, and anvils.
Before, in this thread, I suggested that command blocks have alternate variables for different types of creatures. An alternative, more simple, solution would to be put a valid target field in the Command Block like in the Sensor Block. That would satisfy the same conditions. By default that field would have 'Player' in it, but it could be changed to anything else.
Is there a command that can stop people from griefing?
Griefing is multifold.
You can force them into adventure mode in order to prevent them from breaking blocks.
/gamemode adventure [playername]
However, without mods, you can't prevent them from placing blocks (inappropriate signs, lava, water, TNT, offensive imagery, gravel traps, etc.). Nor can you prevent them from creeper kiting or verbal griefing.
Rollback Post to RevisionRollBack
If you stack a Desert Temple on the top of a Jungle Temple which is on the top of two churches you get a megazord
Can it add a new target(example: @t) which is when someone is triggering the command block, the command makes effect on that person.
Sample Command: /tp @t spawn Effect: It makes the player who triggers it to the spawn point. This should be helpful for all server makers, @p(nearest player) will not take effect when someone is nearer the command block than you. It is very annoying as you can't teleport yourself but teleport others.
I hope this can be add in future updates!
EDIT: One more thing, can add a command on SMP server to enable us to switch pvp without restart server? example command: /pvp on|off