Does Necrotic Ooze take the effect of each individual card in the grave or just each specific effect? For example, if I have four of Kozilek's Translator in GY, can I then activate the effects once for each in GY with Necrotic Ooze, or a total of one time only for that particular effect?
If two or more of a given creature card occur among all graveyards (not just in yours), Necrotic Ooze will have all activated abilities (not: effects) of each one of them. Thus, for example, if there are four Kozilek's Translator cards among all graveyards, Necrotic Ooze will have four instances of "Pay 1 life: Add C. Activate only once each turn." this way (C.R. 108.1), and each such instance works separately (C.R. 113.2c), meaning each one can be activated no more than once each turn (see also C.R. 602.5c).
EDIT: Edited after comment 3 was posted.
EDIT (Apr. 30, 2021): Edited to conform to update with Strixhaven.
EDIT: Edited after comment 3 was posted.
EDIT (Apr. 30, 2021): Edited to conform to update with Strixhaven.