I was making a procedure for which the player has to complete an advancement, in this case beating the Ender Dragon. However, as I began making the procedure, I noticed that the 'has provided entity completed achievement' block had no possible achievements to choose from. So did the 'add achievement to provided entity' block. I tested this by creating an Mcreator advancement, and it had no trouble detecting that. This issue was not present in 1.8.2, but for some reason it was in 1.8.3.