Upon casting on a standard lane minion, the target permanently gains Promoted and Turret Shield. It greatly increases their power, grants them total immunity to magic damage and reduced turret damage. All gold gained by the minion goes to the champion who promoted it. Super minionscannot be promoted.
Melee minion has the most dps of the three and is best used as support for last hitting. Due to the heavy DPS it offers, Melee minion can easily chunk down the minions health to safely last hit.
Caster minion having the most range of the three and is best used to offer more aggro damage if the enemy attacks its ally. Despite being the squishiest and having the lowest DPS, the 600 range the Caster minion offers easily allows it to damage the enemy champions easier and safer.
Siege minion being the tankiest of them all is best used as a self-pushing minion. Due to the difficulty of destroying the Siege minion and the heavy attack damage it brings, it can potentially net last hits without even thinking about it as well and last a long time causing it to inevitably reach the enemy turret if left unhindered.