Trollhide — ruling 1

Trollhide needs to be attached to the creature as the ability that creates the regeneration shield is activated, but after that, the regeneration shield will be created and remain in effect even if Trollhide is no longer attached to the creature.

Trollhide — ruling 2

Activating the ability granted to the enchanted creature causes a “regeneration shield” to be created for it. The next time that creature would be destroyed that turn, the regeneration shield is used up instead. This works only if the creature is dealt lethal damage, dealt damage from a source with deathtouch, or affected by a spell or ability that says to “destroy” it. Other effects that cause the creature to be put into the graveyard (such as reducing its toughness to 0 or sacrificing it) don’t destroy it, so regeneration won’t save it. If it hasn’t been used, the regeneration shield goes away as the turn ends.

Trollhide — ruling 3

To work, the regeneration shield must be created before the enchanted creature is destroyed. This usually means activating its ability during the declare blockers step, or in response to a spell or ability that would destroy it.

Trollhide — ruling 4

If the enchanted creature is dealt lethal damage and is dealt damage by a source with deathtouch during the same combat damage step, a single regeneration shield will save it.

Trollhide : règles, fonctionnement et interactions (MTG)

Trollhide 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

Enchant creature Enchanted creature gets +2/+2 and has ": Regenerate this creature." (The next time the creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

How it works : Trollhide

Original English text — Wizards of the Coast / Scryfall

#1July 1, 2013· Wizards of the Coast
Trollhide needs to be attached to the creature as the ability that creates the regeneration shield is activated, but after that, the regeneration shield will be created and remain in effect even if Trollhide is no longer attached to the creature.
No other card is named in this ruling.
#2September 22, 2011· Wizards of the Coast
Activating the ability granted to the enchanted creature causes a “regeneration shield” to be created for it. The next time that creature would be destroyed that turn, the regeneration shield is used up instead. This works only if the creature is dealt lethal damage, dealt damage from a source with deathtouch, or affected by a spell or ability that says to “destroy” it. Other effects that cause the creature to be put into the graveyard (such as reducing its toughness to 0 or sacrificing it) don’t destroy it, so regeneration won’t save it. If it hasn’t been used, the regeneration shield goes away as the turn ends.
No other card is named in this ruling.
#3September 22, 2011· Wizards of the Coast
To work, the regeneration shield must be created before the enchanted creature is destroyed. This usually means activating its ability during the declare blockers step, or in response to a spell or ability that would destroy it.
No other card is named in this ruling.
#4September 22, 2011· Wizards of the Coast
If the enchanted creature is dealt lethal damage and is dealt damage by a source with deathtouch during the same combat damage step, a single regeneration shield will save it.
No other card is named in this ruling.