To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of this ability)
6 mana is certainly a lot, but the beauty of it is that it gives you a great mana sink, something you usually want, and the creature it makes is no joke either, it can be a real problem on offense or defense for you
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Real life in Ravnica
Her ability Sweet Dreams is what causes her to sit in a weird spot
With any extra creature, for example, Village Rites, Street Wraith, and Corrupted Conviction do the same thing for two mana