What it does
Modular is a keyword found mostly on artifact creatures. A creature with "Modular N" enters the battlefield with N +1/+1 counters on it. When it dies, you may move those counters onto another artifact creature you control. So a Modular creature is both a body now and a way to buff a future artifact creature later, giving it built-in resilience to removal.
The nuance people miss: the counters move on death, but the new home must be another artifact creature, and the ability is a triggered ability that targets—so if there's no legal artifact creature when it dies, the counters are simply lost. Also, all the current counters move, not just the original N, so any counters added later (via proliferate, modular triggers from other dying creatures, etc.) travel along too.
In Commander, Modular shines in artifact-heavy decks, especially with Arcbound creatures, proliferate effects, or sacrifice synergies that let you keep relocating an ever-growing pile of counters.













