Bedlam Reveler

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Prowess
When Bedlam Reveler enters, discard your hand, then draw three cards.

Innistrad Remastered

Shadows over Innistrad Remastered

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Prowess
When Bedlam Reveler enters the battlefield, discard your hand, then draw three cards.

Double Masters 2022

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When Bedlam Reveler enters the battlefield, discard your hand, then draw three cards.

An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered.

Bedlam Reveler's first ability can't reduce the {R}{R} in its cost.

If you have no cards in hand when Bedlam Reveler enters the battlefield, you just draw three cards.

Prowess is a keyword ability that means "Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn."

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Bedlam Reveler). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.