If I cast Retreat on my own unit and respond by casting another Retreat on the same unit while the first is on the stack, can I channel 2 runes using the same creature?

Ruling: No, you cannot channel 2 runes this way. Only 1 rune can be channeled.

Nuances:

• Retreat specifies that the owner of the target channels a rune, but the owner cannot be defined on resolution because the unit is already in your hand (not on the battlefield) when the second Retreat resolves.