Muraganda Petroglyphs — ruling 1

Any text on a creature is an ability, even if that text isn't currently applicable (such as a cycling ability of a creature).

Muraganda Petroglyphs — ruling 2

If a land with a basic land type becomes a creature, the intrinsic mana ability it has stops Muraganda Petroglyphs from applying to it.

Muraganda Petroglyphs — ruling 3

If an effect says that an affected creature "has" or "gains" an ability, Muraganda Petroglyphs won't apply to that creature because it has gained an ability. If an effect simply says that something is true of an affected creature (such as "target creature can't be blocked this turn") then that effect isn't causing the creature to gain an ability.

Muraganda Petroglyphs — ruling 4

Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature with no abilities may become lethal if that creature gains an ability or Muraganda Petroglyphs leaves the battlefield during that turn.

Muraganda Petroglyphs : règles, fonctionnement et interactions (MTG)

Muraganda Petroglyphs 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

Creatures with no abilities get +2/+2.

How it works : Muraganda Petroglyphs

Original English text — Wizards of the Coast / Scryfall

#1March 19, 2021· Wizards of the Coast
Any text on a creature is an ability, even if that text isn't currently applicable (such as a cycling ability of a creature).
No other card is named in this ruling.
#2March 19, 2021· Wizards of the Coast
If a land with a basic land type becomes a creature, the intrinsic mana ability it has stops Muraganda Petroglyphs from applying to it.
No other card is named in this ruling.
#3March 19, 2021· Wizards of the Coast
If an effect says that an affected creature "has" or "gains" an ability, Muraganda Petroglyphs won't apply to that creature because it has gained an ability. If an effect simply says that something is true of an affected creature (such as "target creature can't be blocked this turn") then that effect isn't causing the creature to gain an ability.
No other card is named in this ruling.
#4March 19, 2021· Wizards of the Coast
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature with no abilities may become lethal if that creature gains an ability or Muraganda Petroglyphs leaves the battlefield during that turn.
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Muraganda Petroglyphs.

Great Fang Chroniclers

Double team {3}{G}: Conjure a card named Muraganda Petroglyphs onto the battlefield, then this creature loses this ability. Activate only as a sorcery.