diff --git a/app/blueprints/api/v1/grid_character_blueprint.rb b/app/blueprints/api/v1/grid_character_blueprint.rb
index 4ef5e97..4ecf072 100644
--- a/app/blueprints/api/v1/grid_character_blueprint.rb
+++ b/app/blueprints/api/v1/grid_character_blueprint.rb
@@ -11,35 +11,30 @@ module Api
       view :nested do
         fields :position, :uncap_level, :perpetuity
 
-        field :transcendence_step, if: ->(_fn, obj, _opt) {
+        field :transcendence_step, if: lambda { |_fn, obj, _opt|
           obj.character.ulb
         } do |c|
           c.transcendence_step
         end
 
-        field :awakening, if: ->(_fn, obj, _opt) {
-          !obj[:awakening].nil?
-        } do |c|
-          {
-            type: c.awakening[:type],
-            level: c.awakening[:level]
-          }
+        field :awakening do |c|
+          c.awakening
         end
 
-        field :over_mastery, if: ->(_fn, obj, _opt) {
+        field :over_mastery, if: lambda { |_fn, obj, _opt|
           !obj.ring1['modifier'].nil? && !obj.ring2['modifier'].nil?
         } do |c|
           rings = []
 
-          rings.push(c.ring1) if !c.ring1['modifier'].nil?
-          rings.push(c.ring2) if !c.ring2['modifier'].nil?
-          rings.push(c.ring3) if !c.ring3['modifier'].nil?
-          rings.push(c.ring4) if !c.ring4['modifier'].nil?
+          rings.push(c.ring1) unless c.ring1['modifier'].nil?
+          rings.push(c.ring2) unless c.ring2['modifier'].nil?
+          rings.push(c.ring3) unless c.ring3['modifier'].nil?
+          rings.push(c.ring4) unless c.ring4['modifier'].nil?
 
           rings
         end
 
-        field :aetherial_mastery, if: ->(_fn, obj, _opt) {
+        field :aetherial_mastery, if: lambda { |_fn, obj, _opt|
           !obj.earring['modifier'].nil?
         } do |c|
           c.earring
@@ -52,6 +47,10 @@ module Api
         include_view :nested
         association :party, blueprint: PartyBlueprint, view: :minimal
       end
+
+      view :destroyed do
+        fields :position, :created_at, :updated_at
+      end
     end
   end
 end
diff --git a/app/blueprints/api/v1/grid_weapon_blueprint.rb b/app/blueprints/api/v1/grid_weapon_blueprint.rb
index a2ff815..3e409e8 100644
--- a/app/blueprints/api/v1/grid_weapon_blueprint.rb
+++ b/app/blueprints/api/v1/grid_weapon_blueprint.rb
@@ -43,6 +43,10 @@ module Api
         include_view :nested
         association :party, blueprint: PartyBlueprint, view: :minimal
       end
+
+      view :destroyed do
+        fields :mainhand, :position, :created_at, :updated_at
+      end
     end
   end
 end
diff --git a/app/controllers/api/v1/grid_characters_controller.rb b/app/controllers/api/v1/grid_characters_controller.rb
index 347ef93..74f521e 100644
--- a/app/controllers/api/v1/grid_characters_controller.rb
+++ b/app/controllers/api/v1/grid_characters_controller.rb
@@ -6,8 +6,8 @@ module Api
       attr_reader :party, :incoming_character, :current_characters
 
       before_action :find_party, only: :create
-      before_action :set, only: [:update, :destroy]
-      before_action :check_authorization, only: [:update, :destroy]
+      before_action :set, only: %i[update destroy]
+      before_action :check_authorization, only: %i[update destroy]
       before_action :find_incoming_character, only: :create
       before_action :find_current_characters, only: :create
 
@@ -21,17 +21,16 @@ module Api
           conflict_view = render_conflict_view(conflict_characters, incoming_character, character_params[:position])
           render json: conflict_view
         else
-          # Replace the grid character in the position if it is already filled
+          # Destroy the grid character in the position if it is already filled
           if GridCharacter.where(party_id: party.id, position: character_params[:position]).exists?
             character = GridCharacter.where(party_id: party.id, position: character_params[:position]).limit(1)[0]
-            character.character_id = incoming_character.id
-
-            # Otherwise, create a new grid character
-          else
-            character = GridCharacter.create!(character_params.merge(party_id: party.id,
-                                                                     character_id: incoming_character.id))
+            character.destroy
           end
 
+          # Then, create a new grid character
+          character = GridCharacter.create!(character_params.merge(party_id: party.id,
+                                                                   character_id: incoming_character.id))
+
           if character.save!
             grid_character_view = render_grid_character_view(character)
             render json: grid_character_view, status: :created
@@ -41,7 +40,7 @@ module Api
 
       def update
         mastery = {}
-        [:ring1, :ring2, :ring3, :ring4, :earring, :awakening].each do |key|
+        %i[ring1 ring2 ring3 ring4 earring awakening].each do |key|
           value = character_params.to_h[key]
           mastery[key] = value unless value.nil?
         end
@@ -49,8 +48,10 @@ module Api
         @character.attributes = character_params.merge(mastery)
 
         if @character.save
+          ap 'Saved character'
           return render json: GridCharacterBlueprint.render(@character, view: :full) if @character.save
         else
+          ap 'Could not save'
           render_validation_error_response(@character)
         end
       end
@@ -94,7 +95,10 @@ module Api
       end
 
       # TODO: Implement removing characters
-      def destroy; end
+      def destroy
+        render_unauthorized_response if @character.party.user != current_user
+        return render json: GridCharacterBlueprint.render(@character, view: :destroyed) if @character.destroy
+      end
 
       private
 
@@ -122,7 +126,7 @@ module Api
       end
 
       def set
-        @character = GridCharacter.find(character_params[:id])
+        @character = GridCharacter.find(params[:id])
       end
 
       def find_incoming_character
@@ -142,9 +146,9 @@ module Api
       def character_params
         params.require(:character).permit(:id, :party_id, :character_id, :position,
                                           :uncap_level, :transcendence_step, :perpetuity,
-                                          :ring1 => [:modifier, :strength], :ring2 => [:modifier, :strength],
-                                          :ring3 => [:modifier, :strength], :ring4 => [:modifier, :strength],
-                                          :earring => [:modifier, :strength], :awakening => [:type, :level])
+                                          ring1: %i[modifier strength], ring2: %i[modifier strength],
+                                          ring3: %i[modifier strength], ring4: %i[modifier strength],
+                                          earring: %i[modifier strength], awakening: %i[type level])
       end
 
       def resolve_params
diff --git a/app/controllers/api/v1/grid_weapons_controller.rb b/app/controllers/api/v1/grid_weapons_controller.rb
index 94c9563..7282161 100644
--- a/app/controllers/api/v1/grid_weapons_controller.rb
+++ b/app/controllers/api/v1/grid_weapons_controller.rb
@@ -3,7 +3,7 @@
 module Api
   module V1
     class GridWeaponsController < Api::V1::ApiController
-      before_action :set, except: %w[create update_uncap_level destroy]
+      before_action :set, except: %w[create update_uncap_level]
 
       attr_reader :party, :incoming_weapon
 
@@ -56,7 +56,10 @@ module Api
       end
 
       # TODO: Implement removing characters
-      def destroy; end
+      def destroy
+        render_unauthorized_response if @weapon.party.user != current_user
+        return render json: GridCharacterBlueprint.render(@weapon, view: :destroyed) if @weapon.destroy
+      end
 
       def update_uncap_level
         weapon = GridWeapon.find(weapon_params[:id])
@@ -115,15 +118,15 @@ module Api
       # Render the conflict view as a string
       def render_conflict_view(conflict_weapon, incoming_weapon, incoming_position)
         ConflictBlueprint.render(nil, view: :weapons,
-                                 conflict_weapon: conflict_weapon,
-                                 incoming_weapon: incoming_weapon,
-                                 incoming_position: incoming_position)
+                                      conflict_weapon: conflict_weapon,
+                                      incoming_weapon: incoming_weapon,
+                                      incoming_position: incoming_position)
       end
 
       def render_grid_weapon_view(grid_weapon, conflict_position)
         GridWeaponBlueprint.render(grid_weapon, view: :full,
-                                   root: :grid_weapon,
-                                   meta: { replaced: conflict_position })
+                                                root: :grid_weapon,
+                                                meta: { replaced: conflict_position })
       end
 
       def save_weapon(weapon)
diff --git a/app/models/grid_character.rb b/app/models/grid_character.rb
index b3f7f38..733fe00 100644
--- a/app/models/grid_character.rb
+++ b/app/models/grid_character.rb
@@ -8,8 +8,8 @@ class GridCharacter < ApplicationRecord
 
   validate :awakening_level, on: :update
   validate :transcendence, on: :update
-  validate :over_mastery_attack, on: :update
-  validate :over_mastery_hp, on: :update
+  validate :validate_over_mastery_values, on: :update
+  validate :validate_aetherial_mastery_value, on: :update
   validate :over_mastery_attack_matches_hp, on: :update
 
   ##### Amoeba configuration
@@ -30,9 +30,9 @@ class GridCharacter < ApplicationRecord
   end
 
   def transcendence
-    errors.add(:transcendence_step, 'character has no transcendence') if transcendence_step > 0 && !character.ulb
+    errors.add(:transcendence_step, 'character has no transcendence') if transcendence_step.positive? && !character.ulb
     errors.add(:transcendence_step, 'transcendence step too high') if transcendence_step > 5 && character.ulb
-    errors.add(:transcendence_step, 'transcendence step too low') if transcendence_step < 0 && character.ulb
+    errors.add(:transcendence_step, 'transcendence step too low') if transcendence_step.negative? && character.ulb
   end
 
   def over_mastery_attack
@@ -54,6 +54,26 @@ class GridCharacter < ApplicationRecord
                'over mastery attack and hp values do not match')
   end
 
+  def validate_over_mastery_values
+    [ring1, ring2, ring3, ring4].each_with_index do |ring, index|
+      next if ring['modifier'].nil?
+
+      modifier = over_mastery_modifiers[ring['modifier']]
+      check_value({ "ring#{index}": { ring[modifier] => ring['strength'] } },
+                  'over_mastery')
+    end
+  end
+
+  def validate_aetherial_mastery_value
+    return if earring['modifier'].nil?
+
+    return unless earring['modifier'].positive?
+
+    modifier = aetherial_mastery_modifiers[earring['modifier']].to_sym
+    check_value({ "earring": { modifier => earring['strength'] } },
+                'aetherial_mastery')
+  end
+
   def character
     Character.find(character_id)
   end
@@ -64,6 +84,124 @@ class GridCharacter < ApplicationRecord
 
   private
 
+  def check_value(property, type)
+    # Input format
+    # { ring1: { atk: 300 } }
+
+    key = property.keys.first
+    modifier = property[key].keys.first
+
+    return if modifier.nil?
+
+    case type
+    when 'over_mastery'
+      errors.add(key, 'invalid value') unless over_mastery_values.include?(key['strength'])
+    when 'aetherial_mastery'
+      errors.add(key, 'value too low') if aetherial_mastery_values[modifier][:min] > self[key]['strength']
+      errors.add(key, 'value too high') if aetherial_mastery_values[modifier][:max] < self[key]['strength']
+    end
+  end
+
+  def over_mastery_modifiers
+    {
+      1 => 'atk',
+      2 => 'hp',
+      3 => 'debuff_success',
+      4 => 'skill_cap',
+      5 => 'ca_dmg',
+      6 => 'ca_cap',
+      7 => 'stamina',
+      8 => 'enmity',
+      9 => 'crit',
+      10 => 'da',
+      11 => 'ta',
+      12 => 'def',
+      13 => 'heal',
+      14 => 'debuff_resist',
+      15 => 'dodge'
+    }
+  end
+
+  def over_mastery_values
+    {
+      atk: [300, 600, 900, 1200, 1500, 1800, 2100, 2400, 2700, 3000],
+      hp: [150, 300, 450, 600, 750, 900, 1050, 1200, 1350, 1500],
+      debuff_success: [6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
+      skill_cap: [6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
+      ca_dmg: [10, 12, 14, 16, 18, 20, 22, 24, 27, 30],
+      ca_cap: [6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
+      crit: [10, 12, 14, 16, 18, 20, 22, 24, 27, 30],
+      enmity: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+      stamina: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+      def: [6, 7, 8, 9, 10, 12, 14, 16, 18, 20],
+      heal: [3, 6, 9, 12, 15, 18, 21, 24, 27, 30],
+      debuff_resist: [6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
+      dodge: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
+      da: [6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
+      ta: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+    }
+  end
+
+  def aetherial_mastery_modifiers
+    {
+      1 => 'da',
+      2 => 'ta',
+      3 => 'ele_atk',
+      4 => 'ele_resist',
+      5 => 'stamina',
+      6 => 'enmity',
+      7 => 'supplemental',
+      8 => 'crit',
+      9 => 'counter_dodge',
+      10 => 'counter_dmg'
+    }
+  end
+
+  def aetherial_mastery_values
+    {
+      da: {
+        min: 10,
+        max: 17
+      },
+      ta: {
+        min: 5,
+        max: 12
+      },
+      ele_atk: {
+        min: 15,
+        max: 22
+      },
+      ele_resist: {
+        min: 5,
+        max: 12
+      },
+      stamina: {
+        min: 5,
+        max: 12
+      },
+      enmity: {
+        min: 5,
+        max: 12
+      },
+      supplemental: {
+        min: 5,
+        max: 12
+      },
+      crit: {
+        min: 18,
+        max: 35
+      },
+      counter_dodge: {
+        min: 5,
+        max: 12
+      },
+      counter_dmg: {
+        min: 10,
+        max: 17
+      }
+    }
+  end
+
   def atk_values
     [300, 600, 900, 1200, 1500, 1800, 2100, 2400, 2700, 3000]
   end
diff --git a/config/routes.rb b/config/routes.rb
index ee59a61..8b3b570 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -8,8 +8,8 @@ Rails.application.routes.draw do
     namespace :v1 do
       resources :parties, only: %i[index create update destroy]
       resources :users, only: %i[create update show]
-      resources :grid_weapons, only: [:update]
-      resources :grid_characters, only: [:update]
+      resources :grid_weapons, only: %i[update destroy]
+      resources :grid_characters, only: %i[update destroy]
       resources :favorites, only: [:create]
 
       get 'users/info/:id', to: 'users#info'