Modular

Modular is a keyword ability that causes a permanent to enter the battlefield with a number of +1/+1 counters. When that permanent dies, its controller may put a +1/+1 counter onto an artifact creature for each +1/+1 counter the permanent had on it when it died.

History
Modular first appeared in Darksteel and Fifth Dawn. Until the release of Modern Horizons, the only creatures with Modular also had "Arcbound" in the title. The first non-creature card with Modular,, was printed in Modern Horizons 2. Star Pupil from Strixhaven: School of Mages has a similar ability, but when it dies, all counters on it of any type can be moved to any creature its controller controls.

Rulings

 * If a creature with Modular gets enough -1/-1 counters to make its toughness 0 or cause the damage on it to be lethal, the Modular ability will still give another artifact creature a number of +1/+1 counters equal to the number the Arcbound creature had before it got -1/-1 counters. See rule 704.8.
 * For the enters-the-battlefield ability, the number of counters the permanent gets is equal to the number that follows the word "Modular" on the card.
 * For the leaves-the-battlefield ability, the number of +1/+1 counters on the permanent at the time it left the battlefield is what's relevant; the number after "Modular" doesn't matter.
 * When a creature with Modular dies, you may put a number of +1/+1 counters equal to the number it had onto a single target artifact creature. You can't split them among two or more artifact creatures, or put less than the number of counters it had when it died, unless you choose not to use the ability.