Belltower Beast of Wrath

Blue/Black Guardian (When this creature enters
the field it targets a Blue/Black artifact that you control, when the targeted artifact is destroyed
destroy this creature.)
When Belltower Beast of Wrath enters the field
the targeted artifact transforms into a 0/20
Belltower with Defender, Reach, and Hexproof, the targeted artifact does not heal between turns.
(It is still considered an artifact.)