Main changes in metagame
The biggest changes they did in the Metagame was specifically the introduction to very powerful Steel- type Pokemon pokemon which have the potential to wall of the Psychic types. This introduction made the Steel- typing a very powerful threat in which some Pokemon got into my OU Tier. Metagross is the biggest etagame chager here as Pokemon like Alakzam and Exeggutor can not hit Metagross super effectively and their STAB attacks are are resited and barely scratch it. A lot of Psychic types got nerfed because of this.
Pokemon that got buffed
Charizard, Moltres, and Typhlosion-These 3 fire types still have a very broken SolarBeam attack available to them making them nearly uncounterable though. Steel types are pretty much cannon fodder to these 3. Metagross does have Rock Slide to have a chance at OHKOing Moltres and Charizard.
Metagross, Empoleon, and Aggron- All I've got to say is wow, with these 3 Steel types Psychic types got nerfed incredibly along with a lot of other Special attackers. They single handedly changed the metagame and hurt alot of Pokemon that were in OU for Pixelmon. Their defenses give each of them 10 or more resistances making them solid tanks and pair it with good movepools and good offensive stats and they all become very good sweepers.
Gengar- Wait gengar got buffed!? the answer is yes the question your asking is probablly "How?" The answer is simply the fact that Gengar is not only still the fastest sleep user in Pixelmon but he also got Substitute (Yes Substitute got fixed) Because of this gengar has a way of Taking a hit while dealing major damage to the opponent's Pokemon so expect more use of Gengar in the future of Pixelmon.
Moves that were fixed for competitive battling
Future Sight- This Psychic type move was a one turn move with 100 Base Power, when it was really supposed to be a 2-3 turn move with 100 Base Power, well now its fixed and Psychic is the more preferred move now.
Last Resort- This move was incredibly broken since it had Base 140 Power, now since its fixed Pokemon such as Flareon and Leafeon who really benefited from it pretty much got it taken away from them and now have to rely on Return instead for an offensive attack.
Substitute- Lots of Possibilities have opened up because of this move. The most notable set are Substitute + Leech Seed sets. Though undoubtedly Gengar got the biggest benefit from this move since he normally uses it as setup to take a hit.
(These are just a few of the moves that are fixed)
Who got hurt the most from the changes?
Without a doubt the Psychic types got hurt very badly as some Pokemon fell out of OU and were drawn into BL and UU as they got walled off by Metagross and Empoleon.
My prediction is that we will see more Gengars, Fire types and Steel- types as part of competitive teams in Pixelmon. But what is really necessary is the Nerf on SolarBeam which we unfortunately did not get.