If the target creature is an illegal target as Kimahri's last ability tries to resolve, it won't resolve and none of its effects will happen. You won't put a counter on Kimahri, and Kimahri won't become a copy of anything.
2025-06-06 • wotc
If the copied creature has {X} in its mana cost, X is 0.
2025-06-06 • wotc
If the copied creature is a token, Kimahri copies the original characteristics of that token as stated by the effect that created the token, with the listed exceptions.
2025-06-06 • wotc
Kimahri copies exactly what was printed on the original creature, with the listed exceptions (unless that creature is copying something else or is a token; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or any Auras or Equipment attached to it, or any non-copy effects that have changed its types, color, power and toughness, and so on.
2025-06-06 • wotc
If the copied creature is copying something else, then Kimahri becomes a copy of whatever that creature is copying, with the listed exceptions.
2025-06-06 • wotc