DotSplat

One thing I noticed is that you're not overriding CommonProxy's registerRenderThings method in the ClientProxy class. public class ClientProxy extends CommonProxy { public void registerRenderThings() { should be: public class ClientProxy extends CommonProxy { @Override public void registerRenderThings() {

Try this. check if potion is active, if no then add else combine. if (!player.isPotionActive(potion.id)) player.addPotionEffect(new PotionEffect(potion.id, duration, amplifier, isAmbient)); else { PotionEffect potionEffect = player.getActivePotionEffect(potion); if (potionEffect.getDuration() < duration) potionEffect.combine(new PotionEffect(potion.id, duration, amplifier, isAmbient)); } }