Skithiryx, the Blight Dragon

• WWizards of the Coast2025-09-19
  Official Ruling
  If the regeneration shield is used, Skithiryx isn't destroyed, all damage marked on Skithiryx is healed, it becomes tapped, and it's removed from combat (if applicable).
• WWizards of the Coast2025-09-19
  Official Ruling
  Activating the regeneration ability creates a replacement effect that acts like a shield, replacing the next time Skithiryx would be destroyed that turn. The shield works against effects that try to destroy Skithiryx or lethal damage that would be dealt to Skithiryx.
• WWizards of the Coast2025-09-19
  Official Ruling
  Skithiryx can regenerate even if it isn't in combat, it's already tapped, or it's undamaged.
• WWizards of the Coast2025-09-19
  Official Ruling
  Damage that a creature with infect deals doesn't result in damage being marked on a creature or a player losing life. Instead, it results in that many -1/-1 counters being put on that creature or that many poison counters being given to that player. Damage dealt to planeswalkers still results in that planeswalker losing that many loyalty counters. Damage dealt to battles still results in that battle losing that many defense counters.
• WWizards of the Coast2025-09-19
  Official Ruling
  A player who has ten or more poison counters loses the game. This is a state-based action.
• WWizards of the Coast2025-09-19
  Official Ruling
  Damage from a source with infect is damage in all respects. If the source with infect also has lifelink, damage dealt by that source also causes its controller to gain that much life. Damage from a source with infect can be prevented or redirected. Abilities that trigger on damage being dealt will trigger if a source with infect deals damage, if appropriate.
• WWizards of the Coast2025-09-19
  Official Ruling
  The -1/-1 counters remain on the creature indefinitely. They're not removed if the creature regenerates or the turn ends.

Rulings via Scryfall