Bone Shredder
Creature — Phyrexian Minion
Flying
Echo (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When this creature enters, destroy target nonartifact, nonblack creature.
Ron Spencer
Modern Horizons 2 (MH2)
• #272Rulings
Paying for echo is always optional. When the echo triggered ability resolves, if you can't pay the echo cost or choose not to, you sacrifice that permanent.
(wotc • 2021-06-18)
Your permanent's echo ability will trigger at the beginning of your upkeep if it entered the battlefield since the beginning of your last upkeep, or if you gained control of it since the beginning of your last upkeep.
(wotc • 2021-06-18)
Rulings
Paying for echo is always optional. When the echo triggered ability resolves, if you can't pay the echo cost or choose not to, you sacrifice that permanent.
(wotc • 2021-06-18)
Your permanent's echo ability will trigger at the beginning of your upkeep if it entered the battlefield since the beginning of your last upkeep, or if you gained control of it since the beginning of your last upkeep.
(wotc • 2021-06-18)