.java

Preinit
snw.registerMessage(MessageRegenMana.RegenManaHandler.class, MessageRegenMana.class, 8, Side.SERVER);
snw.registerMessage(MessageSyncMana.ManaSyncHandler.class, MessageSyncMana.class, 9, Side.CLIENT);

Server mana packet
public class MessageRegenMana implements IMessage
{
	int id;
	public MessageRegenMana(){}

	public MessageRegenMana(int id)
	{
		this.id = id;
	}

	@Override
	public void fromBytes(ByteBuf buf)
	{
		this.id = buf.readInt();
	}

	@Override
	public void toBytes(ByteBuf buf)
	{
		buf.writeInt(this.id);
	}

	public static class RegenManaHandler implements IMessageHandler<MessageRegenMana, IMessage>
	{
		@Override
		public IMessage onMessage(MessageRegenMana message, MessageContext ctx)
		{
			EntityPlayer player = (EntityPlayer)ctx.getServerHandler().playerEntity.worldObj.getEntityByID(message.id);
			AAExtendedPlayer props = (AAExtendedPlayer)player.getExtendedProperties(AAExtendedPlayer.EEPName);
			props.addMana(new Mana(ManaType.W, 1));
			props.addMana(new Mana(ManaType.U, 1));
			props.addMana(new Mana(ManaType.B, 1));
			props.addMana(new Mana(ManaType.G, 1));
			props.addMana(new Mana(ManaType.R, 1));

			ArcaneArtificing.snw.sendToAll(new MessageSyncMana(player.getEntityId(), props.getWhiteMana(), props.getBlueMana(), props.getBlackMana(), props.getGreenMana(), props.getRedMana()));
			return null;
		}
	}
}

Client sync packet
public class MessageSyncMana implements IMessage
{
	int id, w, u, b, g, r;

	public MessageSyncMana(){}

	public MessageSyncMana(int id, int w, int u, int b, int g, int r)
	{
		this.id = id;
		this.w = w;
		this.u = u;
		this.b = b;
		this.g = g;
		this.r = r;
	}

	@Override
	public void fromBytes(ByteBuf buf)
	{
		this.id = buf.readInt();
		this.w = buf.readInt();
		this.u = buf.readInt();
		this.b = buf.readInt();
		this.g = buf.readInt();
		this.r = buf.readInt();
	}

	@Override
	public void toBytes(ByteBuf buf)
	{
		buf.writeInt(this.id);
		buf.writeInt(this.w);
		buf.writeInt(this.u);
		buf.writeInt(this.b);
		buf.writeInt(this.g);
		buf.writeInt(this.r);
	}

	public static class ManaSyncHandler implements IMessageHandler<MessageSyncMana, IMessage>
	{
		@Override
		public IMessage onMessage(MessageSyncMana message, MessageContext ctx)
		{
			Entity entity = ArcaneArtificing.proxy.getClientWorld().getEntityByID(message.id);
			if(entity instanceof EntityPlayer)
			{
				EntityPlayer player = (EntityPlayer)entity;
				AAExtendedPlayer props = (AAExtendedPlayer)player.getExtendedProperties(AAExtendedPlayer.EEPName);
				props.setWhiteMana(message.w);
				props.setBlueMana(message.u);
				props.setBlackMana(message.b);
				props.setGreenMana(message.g);
				props.setRedMana(message.r);
			}
			return null;
		}
	}
}

Persistence events
public class ManaPersistence
{
	@SubscribeEvent
	public void persistMana(PlayerEvent.Clone event)
	{
		if(!event.wasDeath)
		{
			EntityPlayer playerOrig = event.original;
			EntityPlayer playerNew = event.entityPlayer;

			AAExtendedPlayer propsOrig = (AAExtendedPlayer)playerOrig.getExtendedProperties(AAExtendedPlayer.EEPName);

			playerNew.registerExtendedProperties(AAExtendedPlayer.EEPName, propsOrig);
		}
	}

	@SubscribeEvent
	public void syncPersistenceToClient(EntityJoinWorldEvent event)
	{
		if(!event.world.isRemote && event.entity instanceof EntityPlayer)
		{
			EntityPlayer player = (EntityPlayer)event.entity;
			AAExtendedPlayer props = (AAExtendedPlayer)player.getExtendedProperties(AAExtendedPlayer.EEPName);
			ArcaneArtificing.snw.sendToAll(new MessageSyncMana(player.getEntityId(), props.getWhiteMana(), props.getBlueMana(), props.getBlackMana(), props.getGreenMana(), props.getRedMana()));
		}
	}
}

Keybind
@SideOnly(Side.CLIENT)
public class GatherManaKeybind extends KeyBinding
{
	public GatherManaKeybind()
	{
		super("key.gatherMana", Keyboard.KEY_G, "key.categories." + AAReference.MODID);
	}

	@SubscribeEvent()
	public void onKeyInput(TickEvent.ClientTickEvent event)
	{
		if(event.phase == TickEvent.Phase.START && this.getIsKeyPressed())
		{
			ArcaneArtificing.snw.sendToServer(new MessageRegenMana(ArcaneArtificing.proxy.getClientPlayer().getEntityId()));
		}
	}
}