That's one heck of a commit you've got there...

I may have got a bit behind with version control. A lot behind, in fact. Maybe I'll go back and split this sometime - then again, I probably won't. But hey, at least it's here!

src/main/java/electroblob/wizardry/advancement/CustomAdvancementTrigger.java

@@ -0,0 +1,81 @@
+package electroblob.wizardry.advancement;
+
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.SetMultimap;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonObject;
+import electroblob.wizardry.Wizardry;
+import net.minecraft.advancements.ICriterionInstance;
+import net.minecraft.advancements.ICriterionTrigger;
+import net.minecraft.advancements.PlayerAdvancements;
+import net.minecraft.advancements.critereon.AbstractCriterionInstance;
+import net.minecraft.entity.player.EntityPlayer;
+import net.minecraft.entity.player.EntityPlayerMP;
+import net.minecraft.util.ResourceLocation;
+
+/**
+ * This class implements a generic custom advancement trigger that can be fired from any point in
+ * the code. This replaces the achievement system in instances where the JSON advancement descriptions
+ * cannot properly capture the advancement-worthy events. Where possible, advancement conditions
+ * should be triggered by JSON descriptions and vanilla advancement triggers.
+ *
+ * @author 12foo
+ * @since 4.1.0
+ */
+public class CustomAdvancementTrigger implements ICriterionTrigger<CustomAdvancementTrigger.Instance> {
+
+    private final ResourceLocation id;
+    private final SetMultimap<PlayerAdvancements, Listener<? extends ICriterionInstance>> listeners = HashMultimap.create();
+
+    /**
+     * This is a dummy criterion instance that does nothing on its own (but it is bound to this
+     * trigger, and via listeners to the player). We later fire this manually when we want the
+     * advancement to happen.
+     */
+    public static class Instance extends AbstractCriterionInstance {
+        public Instance(ResourceLocation triggerId) { 
+            super(triggerId);
+        }
+    }
+
+    public CustomAdvancementTrigger(String name) {
+        super();
+        id = new ResourceLocation(Wizardry.MODID, name);
+    }
+
+    @Override
+    public ResourceLocation getId() {
+        return id;
+    }
+
+    @Override
+    public void addListener(PlayerAdvancements playerAdvancementsIn, Listener<Instance> listener) {
+        listeners.put(playerAdvancementsIn, listener);
+    }
+
+    @Override
+    public void removeListener(PlayerAdvancements playerAdvancementsIn, Listener<Instance> listener) {
+        listeners.remove(playerAdvancementsIn, listener);
+    }
+
+    @Override
+    public void removeAllListeners(PlayerAdvancements playerAdvancementsIn) {
+        listeners.removeAll(playerAdvancementsIn);
+    }
+
+    @Override
+    public Instance deserializeInstance(JsonObject json, JsonDeserializationContext context) {
+        // Every time a trigger with this name is deserialized from the JSON, we just return a new
+        // dummy criterion instance.
+        return new CustomAdvancementTrigger.Instance(id);
+    }
+
+    public void triggerFor(EntityPlayer player) {
+        // Fire our dummy criterion manually on all advancements of the player, thereby granting
+        // the ones that match it.
+        if (player instanceof EntityPlayerMP) {
+            final PlayerAdvancements advances = ((EntityPlayerMP) player).getAdvancements();
+            listeners.get(advances).forEach((listener) -> listener.grantCriterion(advances));
+        }
+    }
+}