Fire Mechanics: using fire is a excellent way to detect when a entity is on the ground.

when fire is setblocked it will not work until it is on the ground.

let's say you want to make Chicken bombs that explode on the ground. use these 2 commands in command blocks put them down like this.



After that put this command in the Repeating command block:

execute @e[type=chicken,name=Bomb] ~ ~ ~ /fill ~ ~ ~ ~ ~ ~ minecraft:fire 1 0

After that put this command in the Chain command block:

execute @e[type=chicken,name=Bomb] ~ ~ ~ detect ~ ~ ~ minecraft:fire -1 /summon minecraft:tnt ~ ~ ~

after that step is done, grab an anvil and name an egg Bomb (with the B in CAPS), then go high in the air and spawn a chicken named Bomb. Watch the Bomb as it slowly floats down. If you watch the the chicken hit the ground you will barely see a block of fire (appear then disappear).

how this work is the REPEATING block is always setting fire; but sense it's not on the ground is just disapears (until the chicken hit the ground. and in the CHAIN block it detect when the chicken is in the fire then it blows up.

The FIRE MECHANICS are awesome!
this works for snowballs, mobs and MORE!!