This list doesnt include cards that make temporary copies that leave play at the end of the turn like Kiki-Jiki, Mirror Breaker or Flameshadow Conjuring
For example, removal-heavy decks tend to have a headache against decks that don't care too much for the battlefield (like control decks), or decks that are happy to fill their graveyard (like reanimator decks), or decks that can sacrifice creatures when their enemies point removal at them (like aristocrat Commander decks)
Massacre Wurm A wrath effect on a (really, really big) stick, Massacre Wurm enjoys being reanimated to kill the table with that life loss ability in decks with Araumi of the Dead Tide or Meren of Clan Nel Toth
If you do, return him to the battlefield transformed under his owners control
Many Naya decks (especially those not run by Hazezon Tamar) are built around the beef
It's also in the colors of artifact support in Azorius so there are tons of cards that will love this thing