Deathcoil Wurm — ruling 1

You can decide to assign damage to the defending player or planeswalker even if the blocking creature has protection from green or damage preventing effects on it.

Deathcoil Wurm — ruling 2

When assigning combat damage, you choose whether you want to assign all damage to blocking creatures, or if you want to assign all of it to the player or planeswalker this creature is attacking. You can't split the damage assignment between them.

Deathcoil Wurm — ruling 3

If blocked by a creature with banding, the defending player decides whether or not the damage is assigned "as though it weren't blocked".

Deathcoil Wurm : règles, fonctionnement et interactions (MTG)

Deathcoil Wurm is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

You may have this creature assign its combat damage as though it weren't blocked.

How it works : Deathcoil Wurm

Original English text — Wizards of the Coast / Scryfall

#1April 27, 2018· Wizards of the Coast
You can decide to assign damage to the defending player or planeswalker even if the blocking creature has protection from green or damage preventing effects on it.
No other card is named in this ruling.
#2April 27, 2018· Wizards of the Coast
When assigning combat damage, you choose whether you want to assign all damage to blocking creatures, or if you want to assign all of it to the player or planeswalker this creature is attacking. You can't split the damage assignment between them.
No other card is named in this ruling.
#3April 27, 2018· Wizards of the Coast
If blocked by a creature with banding, the defending player decides whether or not the damage is assigned "as though it weren't blocked".
No other card is named in this ruling.