Activate Phyrexian Altar by sacrificing Dulcet Sirens, adding {U}.
When Dulcet Sirens dies, Missy's first ability triggers, returning Dulcet Sirens from your graveyard to the battlefield face down as a 2/2 Cyberman artifact creature.
Activate Dulcet Sirens's morph ability by paying {U}, turning it face up.
Repeat.

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite sacrifice triggers

Missy

Phyrexian Altar

Dulcet Sirens

Activate Phyrexian Altar by sacrificing Dulcet Sirens, adding {U}.
When Dulcet Sirens dies, Yedora triggers, returning Dulcet Sirens from your graveyard to the battlefield face down as a Forest land.
Activate Dulcet Sirens by tapping it, adding {G}.
Activate Dulcet Sirens's morph ability by paying {U}, turning it face up.
Repeat.

Infinite green mana

Infinite landfall triggers

Yedora, Grave Gardener

Combos with "Dulcet Sirens"