diff --git a/src/pocketmine/Player.php b/src/pocketmine/Player.php
index 5fd602a56..8536bea93 100644
--- a/src/pocketmine/Player.php
+++ b/src/pocketmine/Player.php
@@ -1656,6 +1656,12 @@ class Player extends Human implements CommandSender, InventoryHolder, IPlayer{
 				}
 
 				if($target instanceof Entity and $this->getGamemode() !== Player::VIEW and $this->blocked === false and $this->dead !== true and $target->dead !== true){
+					if($target instanceof DroppedItem or $target instanceof Arrow){
+						$this->kick("Attempting to attack an invalid entity");
+						$this->server->getLogger()->warning("Player ". $this->getName() ." tried to attack an invalid entity");
+						return;
+					}
+
 					$item = $this->inventory->getItemInHand();
 					$damageTable = [
 						Item::WOODEN_SWORD => 4,
diff --git a/src/pocketmine/block/Block.php b/src/pocketmine/block/Block.php
index 677d0b682..f5e4b4f1b 100644
--- a/src/pocketmine/block/Block.php
+++ b/src/pocketmine/block/Block.php
@@ -28,8 +28,10 @@ use pocketmine\entity\Villager;
 use pocketmine\entity\Zombie;
 use pocketmine\item\Item;
 use pocketmine\level\Level;
+use pocketmine\level\MovingObjectPosition;
 use pocketmine\level\Position;
 use pocketmine\math\AxisAlignedBB;
+use pocketmine\math\Vector3;
 use pocketmine\metadata\Metadatable;
 use pocketmine\metadata\MetadataValue;
 use pocketmine\Player;
@@ -844,6 +846,88 @@ abstract class Block extends Position implements Metadatable{
 		);
 	}
 
+	public function calculateIntercept(Vector3 $pos1, Vector3 $pos2){
+		$bb = $this->getBoundingBox();
+		if($bb === null){
+			return null;
+		}
+
+		$v1 = $pos1->getIntermediateWithXValue($pos2, $bb->minX);
+		$v2 = $pos1->getIntermediateWithXValue($pos2, $bb->maxX);
+		$v3 = $pos1->getIntermediateWithYValue($pos2, $bb->minY);
+		$v4 = $pos1->getIntermediateWithYValue($pos2, $bb->maxY);
+		$v5 = $pos1->getIntermediateWithZValue($pos2, $bb->minZ);
+		$v6 = $pos1->getIntermediateWithZValue($pos2, $bb->maxZ);
+
+		if($v1 !== null and !$bb->isVectorInYZ($v1)){
+			$v1 = null;
+		}
+
+		if($v2 !== null and !$bb->isVectorInYZ($v2)){
+			$v2 = null;
+		}
+
+		if($v3 !== null and !$bb->isVectorInXZ($v3)){
+			$v3 = null;
+		}
+
+		if($v4 !== null and !$bb->isVectorInXZ($v4)){
+			$v4 = null;
+		}
+
+		if($v5 !== null and !$bb->isVectorInXY($v5)){
+			$v5 = null;
+		}
+
+		if($v6 !== null and !$bb->isVectorInXY($v6)){
+			$v6 = null;
+		}
+
+		$vector = $v1;
+
+		if($v2 !== null and ($vector === null or $pos1->distanceSquared($v2) < $pos1->distanceSquared($vector))){
+			$vector = $v2;
+		}
+
+		if($v3 !== null and ($vector === null or $pos1->distanceSquared($v3) < $pos1->distanceSquared($vector))){
+			$vector = $v3;
+		}
+
+		if($v4 !== null and ($vector === null or $pos1->distanceSquared($v4) < $pos1->distanceSquared($vector))){
+			$vector = $v4;
+		}
+
+		if($v5 !== null and ($vector === null or $pos1->distanceSquared($v5) < $pos1->distanceSquared($vector))){
+			$vector = $v5;
+		}
+
+		if($v6 !== null and ($vector === null or $pos1->distanceSquared($v6) < $pos1->distanceSquared($vector))){
+			$vector = $v6;
+		}
+
+		if($vector === null){
+			return null;
+		}
+
+		$f = -1;
+
+		if($vector === $v1){
+			$f = 4;
+		}elseif($vector === $v2){
+			$f = 5;
+		}elseif($vector === $v3){
+			$f = 0;
+		}elseif($vector === $v4){
+			$f = 1;
+		}elseif($vector === $v5){
+			$f = 2;
+		}elseif($vector === $v6){
+			$f = 3;
+		}
+
+		return MovingObjectPosition::fromBlock($this->x, $this->y, $this->z, $f, $vector->add($this->x, $this->y, $this->z));
+	}
+
 	/**
 	 * Places the Block, using block space and block target, and side. Returns if the block has been placed.
 	 *
diff --git a/src/pocketmine/entity/Living.php b/src/pocketmine/entity/Living.php
index 6021d447d..3be887443 100644
--- a/src/pocketmine/entity/Living.php
+++ b/src/pocketmine/entity/Living.php
@@ -58,6 +58,11 @@ abstract class Living extends Entity implements Damageable{
 
 	public abstract function getName();
 
+	public function hasLineOfSight(Entity $entity){
+		//TODO: head height
+		return $this->getLevel()->rayTraceBlocks(new Vector3($this->x, $this->y + $this->height, $this->z), new Vector3($entity->x, $entity->y + $entity->height, $entity->z)) === null;
+	}
+
 	public function attack($damage, $source = EntityDamageEvent::CAUSE_MAGIC){
 		//TODO: attack tick limit
 		$pk = new EntityEventPacket();
diff --git a/src/pocketmine/level/Level.php b/src/pocketmine/level/Level.php
index c70ddfe4b..15e8253c5 100644
--- a/src/pocketmine/level/Level.php
+++ b/src/pocketmine/level/Level.php
@@ -723,6 +723,78 @@ class Level implements ChunkManager, Metadatable{
 		return $collides;
 	}
 
+	/*
+	public function rayTraceBlocks(Vector3 $pos1, Vector3 $pos2, $flag = false, $flag1 = false, $flag2 = false){
+		if(!is_nan($pos1->x) and !is_nan($pos1->y) and !is_nan($pos1->z)){
+			if(!is_nan($pos2->x) and !is_nan($pos2->y) and !is_nan($pos2->z)){
+				$x1 = (int) $pos1->x;
+				$y1 = (int) $pos1->y;
+				$z1 = (int) $pos1->z;
+				$x2 = (int) $pos2->x;
+				$y2 = (int) $pos2->y;
+				$z2 = (int) $pos2->z;
+
+				$block = $this->getBlock(new Vector3($x1, $y1, $z1));
+
+				if(!$flag1 or $block->getBoundingBox() !== null){
+					$ob = $block->calculateIntercept($pos1, $pos2);
+					if($ob !== null){
+						return $ob;
+					}
+				}
+
+				$movingObjectPosition = null;
+
+				$k = 200;
+
+				while($k-- >= 0){
+					if(is_nan($pos1->x) or is_nan($pos1->y) or is_nan($pos1->z)){
+						return null;
+					}
+
+					if($x1 === $x2 and $y1 === $y2 and $z1 === $z2){
+						return $flag2 ? $movingObjectPosition : null;
+					}
+
+					$flag3 = true;
+					$flag4 = true;
+					$flag5 = true;
+
+					$i = 999;
+					$j = 999;
+					$k = 999;
+
+					if($x1 > $x2){
+						$i = $x2 + 1;
+					}elseif($x1 < $x2){
+						$i = $x2;
+					}else{
+						$flag3 = false;
+					}
+
+					if($y1 > $y2){
+						$j = $y2 + 1;
+					}elseif($y1 < $y2){
+						$j = $y2;
+					}else{
+						$flag4 = false;
+					}
+
+					if($z1 > $z2){
+						$k = $z2 + 1;
+					}elseif($z1 < $z2){
+						$k = $z2;
+					}else{
+						$flag5 = false;
+					}
+
+					//TODO
+				}
+			}
+		}
+	}
+	*/
+
 	/**
 	 * Gets the Block object on the Vector3 location
 	 *
diff --git a/src/pocketmine/math/AxisAlignedBB.php b/src/pocketmine/math/AxisAlignedBB.php
index ebeb7e92d..8db9aa4f8 100644
--- a/src/pocketmine/math/AxisAlignedBB.php
+++ b/src/pocketmine/math/AxisAlignedBB.php
@@ -264,7 +264,6 @@ class AxisAlignedBB{
 		return $vector->x >= $this->minX and $vector->x <= $this->maxX and $vector->y >= $this->minY and $vector->y <= $this->maxY;
 	}
 
-
 	public function calculateIntercept(Vector3 $pos1, Vector3 $pos2){
 		$v1 = $pos1->getIntermediateWithXValue($pos2, $this->minX);
 		$v2 = $pos1->getIntermediateWithXValue($pos2, $this->maxX);