Sasaya's Essence has a triggered mana ability. Like activated mana abilities, the triggered mana ability doesn't use the stack.

If Sasaya's Essence's controller has four Forests and taps one of them for , the Essence will add for a total of .

The triggered mana ability counts the number of other lands with that same name and adds that much mana. The type (that is, the color of mana or colorless mana) is the same as the mana the land just produced.

If Sasaya's Essence's controller has two Brushlands and taps one of them for , Sasaya's Essence adds another . It won't produce or unless the land was tapped for or instead.

Each Ascendant is legendary in both its unflipped and flipped forms. This means that effects that look for legendary creature cards, such as Time of Need and Captain Sisay, can find an Ascendant.

If Sasaya's Essence's controller has four Mossfire Valley and taps one of them for , the Essence will add three mana (one for each other Mossfire Valley) of any combination of and/or .

You don't need to have seven lands in hand to reveal your hand. You leave your hand revealed until the ability resolves. If you don't have seven or more land cards in your hand at that time, the effect does nothing.

You don't need to tap Sasaya to use its ability, so you can activate the ability on the turn Sasaya comes under your control.