Extremely Slow Zombie — ruling 1

Last strike is opposite of first strike. A creature with last strike deals combat damage after when most creatures deal combat damage. A creature with last strike deals combat damage only if it survives both first-strike and normal combat damage.

Extremely Slow Zombie — ruling 2

If you give first strike to a creature with last strike, it’ll deal combat damage twice: once during first-strike combat damage and again during last-strike combat damage. If you give a creature double strike to a creature with last strike, it’ll deal combat damage three times: once during first-strike combat damage, again during normal combat damage, and again during last-strike damage. Essentially, double strike + last strike = triple strike.

Extremely Slow Zombie : règles, fonctionnement et interactions (MTG)

Extremely Slow Zombie 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

Last strike (This creature deals combat damage after creatures without last strike.)

How it works : Extremely Slow Zombie

Original English text — Wizards of the Coast / Scryfall

#1January 19, 2018· Wizards of the Coast
Last strike is opposite of first strike. A creature with last strike deals combat damage after when most creatures deal combat damage. A creature with last strike deals combat damage only if it survives both first-strike and normal combat damage.
No other card is named in this ruling.
#2January 19, 2018· Wizards of the Coast
If you give first strike to a creature with last strike, it’ll deal combat damage twice: once during first-strike combat damage and again during last-strike combat damage. If you give a creature double strike to a creature with last strike, it’ll deal combat damage three times: once during first-strike combat damage, again during normal combat damage, and again during last-strike damage. Essentially, double strike + last strike = triple strike.
No other card is named in this ruling.