Minecraft Story Mode:Command Block

The command block is a powerful block and a key component to the plot.

Ender dragon fight
The command block is first known to be used by the Order of the Stone to kill the ender dragon. It was used by Soren to erase the ender dragon from existance. Although how the command block was used before is unknown, Soren made it clear that by the time the ender dragon fight happened, the team was already dependent on using it.

Ivor's far lands base
The command block was used by Ivor to build his base in far lands.

Wither storm
The wither storm was created by Ivor in the episode 1 of the first season with the use of the command block. The soul sand in the middle of the wither was replaced with command block in order to create a powerful creature.

Trivia

 * The command block is immune to all explosions, including the formidi-bomb.
 * However, Ivor with the use of the command block created an enchantment that is capable of destroying it.
 * The command block pulses before performing an action. This is not seen in vanilla Minecraft.
 * In vanilla Minecraft, the command block is not usable in Survival Mode; however, in Minecraft: Story Mode, it is.