Poppet

A poppet is a doll created as a representation of a person with the intention of casting spells upon that person by way of inflicting those spells upon the doll. Magical poppets are very similar to Voodoo dolls.

Poppets have been used by magic practicers in many different occasions.

Mary Collins' poppet
Mary Collins used a poppet, made of straw, to murder Lady Helen of Mora so that she could take on the singer's form. The witch chanted a spell three times ("Acwele seo mægþ!") while stabbing the effigy. After having put a glamour on herself, Mary Collins went to Camelot and took the poppet with her, for unknown reasons.

When Merlin went to her chambers to give the singer one of Gaius' potions, he saw the poppet and was probably attracted to it by its magic, for ghostly whispers could be heard. The young warlock picked up the effigy and studied it for a while, then he turned his attention to Mary Collins' grimoire. Anyway, he had to quickly put it down when he heard the witch was coming, covering up the evidence that he was snooping (The Dragon's Call).

Arthur's likeness
Morgause, disguised as an old woman, gave Morgana a bracelet with a Phoenix Eye telling her to present it to the Prince as a token of her good wishes. She than had to make a likeness of Arthur and bind it to the gift (the bracelet) using the skills that she taught her.

In her chambers, Morgana created a doll with pieces of wood and cloths, which she then burnt on a candle. As soon as the poppet was reduced to ashes, the Witch put it in a metal box and lighted it again with her magic. Morgana didn't have to chant a spell to set the effigy on fire (a think she probably wouldn't have been able to do, considering her inexperience) but only concentrate her energies on it, as Morgause had taught her. The spell caused the Eye to glow and to start consuming Arthur's life force.

Morgana was forced to repeat it twice because she was interrupted by her maid Gwen. Probably, the Eye could only work if the poppet's ashes, that Morgana kept in the metal box and relight with her magic, were burning (The Eye of the Phoenix).

Morgana's effigy
Merlin, under the effects of an ageing spell and disguised as "Dragoon the Great" or "Old Emrys", entered the castle of Camelot, which had been conquered by Morgana, and the Queen's chambers to cast a powerful spell on a poppet ("Ontende eallne þæs drycræftes hire sawle!"). This enchantment caused the magical doll to burst into flame and start emitting faint ghostly whispers at the edge of awareness. The fire scorched but did not consume the effigy. Emrys hung it under the High Priestess' bed once the fire had gone out.

Merlin's curse had the effect of blocking Morgana's powers, making her unable to use magic. In fact, when Arthur and his followers entered the throne room, Morgana tried to cast a stunning spell, but as she pronounced the incantation, her eyes didn't glow golden and the poppet's whispers could be heard. While the Witch was trying to focus her energies, Merlin concentrated his powers on the poppet, strengthening the enchantment (The Sword in the Stone: Part Two).

It's unknown if Merlin's enchantment is still working, even after Morgana was healed and reanimated by the young dragon Aithusa (The Sword in the Stone: Part Two).