As long as Necrotic Ooze is on the battlefield, it has all activated abilities of all creature cards in all graveyards.
1/1/2011 Necrotic Ooze gains only activated abilities. It doesn’t gain keyword abilities (unless those keyword abilities are activated), triggered abilities, or static abilities.
1/1/2011 Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities; they have colons in their reminder text.
1/1/2011 If an activated ability of a card in a graveyard references the card it’s printed on by name, treat Necrotic Ooze’s version of that ability as though it referenced Necrotic Ooze by name instead. For example, if Cudgel Troll (which says “: Regenerate Cudgel Troll”) is in a graveyard, Necrotic Ooze has the ability “: Regenerate Necrotic Ooze.”