There are a few Pokemon that have the ability to go through a final evolution temporarily while in battle. In Pixelmon 5.1.2. three Pokemon have this ability. Charizard, Venusaur and Blastoise. Mega Evolutions causes a stat buff and can change the actual type of the Poke but the evolution cannot be applied outside of battle.
The Starting Steps
You will need a Mega Bracelet, a Mega Stone and one of those three compatible to start. There will be many random mega evolution boss types throughout your Pixelmon world, you must find one of these and defeat it in battle. As soon as the Poke is defeated, an optional display will oppose the player asking if the Bracelet is to be worn, which is the case needed to trigger Evolution. There is also a small chance of 2.5% that random boss Pokemon may drop the mega stone required. But even so, Mega Boss Pokemon will always drop the Mega Stone appropriate to that type.
Upon obtaining the three requirements, you are now ready to begin. You must place the Mega Stone in the side box when opening up the inventory so it’s being held by the prior evolution. The player must also wear the Mega Bracelet at the same time. Once engaging a battle, select FIGHT, and there will be an extra box titled Mega Evolve. Select this and your Poke will have a short animation script begin, which transforms your poke.
To make your discovering easier, we have identified and compiled a list for where to look for the three types of Mega Bosses.
Venusaur – Mega Venusaur – Land (Plains, Forests, etc)
Charizard – Mega X – Air Constant
Charizard – Mega Y – Air Constant
Blastoise – Mega Blastoise – Water (Oceans, beaches etc)