If I copy a unit with Leblanc legend, does it keep the plus might it had from previous buffs?

No, the copy created by LeBlanc's legend does not keep any +Might from previous buffs.

When you use LeBlanc’s legend ability to create a copy, that new unit enters as a base version of the target. According to RiftJudge FAQ #10455 and the Patch Notes (2026-03-30), copy effects only inherit a unit's "copyable traits," which are its printed characteristics (like base Might and Rules Text).

Buffs are considered "appended or granted" modifications, not part of a unit's printed or copyable traits. Therefore, they are not transferred to the copy.