Models

bad_companion.rb

class BadCompanion < Green
  has_many :companionships, as: :companion
  has_many :greens, through: :companionships
end

companionship.rb

class Companionship < ApplicationRecord
  belongs_to :green
  belongs_to :companion, polymorphic: true
end

good_companion.rb

class GoodCompanion < Green
  has_many :companionships, as: :companion
  has_many :greens, through: :companionships
end

green.rb

class Green < ApplicationRecord
  has_many :companionships
  has_many :bad_companions, through: :companionships, source: :companion, source_type: 'BadCompanion'
  has_many :good_companions, through: :companionships, source: :companion, source_type: 'GoodCompanion'
end