If a showdown has started, can you move units into the battle if you don't have enough might? What if the unit has ganking?

No, you cannot move units into a battlefield during a showdown, regardless of their Might or whether they have the Ganking ability.

According to Rule 143.1.c, the Standard Move action (which is the action used to move units) cannot be performed during a showdown. Because Ganking is a passive ability that specifically adds new options to a unit's Standard Move (as stated in Rule 736.1.c), it does not bypass the restriction that prevents Standard Moves from occurring during a showdown.

In summary:

  • Standard Move Restriction: Standard Moves are prohibited during a showdown (Rule 143.1.c).
  • Ganking: Ganking only provides new destination options for a Standard Move; it does not grant the ability to move during a showdown or override the timing restrictions of the Standard Move action (Rule 736.1.c.1).
  • Might: A unit's Might value has no bearing on whether it is legally allowed to move.