When I have Elder Dragon and I play a unit with 3 might to a battlefield, can I split the 3 might of my unit to kill 3 different units on that battlefield?
Yes, you can.
Because you control Elder Dragon, its ability ("Any amount of your damage is enough to kill enemy units") modifies the definition of "lethal damage" for any damage you deal. Normally, you must assign lethal damage (damage equal to or exceeding a unit's Might) to a unit before moving to the next one (Rule 460.2.c.3). With Elder Dragon in play, 1 damage is considered lethal for your damage.
During the combat damage step, when you assign the 3 Might from your unit:
- Rule 460.2.c.3 requires that you assign "lethal damage" to a unit before moving to the next one.
- Because Elder Dragon makes 1 damage "lethal," you satisfy the requirement of assigning "lethal damage" to a unit by assigning just 1 damage.
- As long as you have enough total Might (3) to cover the lethal requirement for each of the three units (1 damage each), you can assign 1 damage to the first unit (killing it), 1 to the second (killing it), and 1 to the third (killing it).
This interaction is confirmed by RiftJudge FAQ #10071 and #8762, which clarify that with Elder Dragon, you can distribute your total Might one-by-one to clear multiple units on the board.