If that creature is no longer on the battlefield when Close Encounter resolves, use that creature's power as it last existed on the battlefield to determine how much damage is dealt
And if you'd rather focus more on non- Final Fantasy Birds in Magic (because the chocobos are flightless Birds), there are cards like Watcher of the SpheresWatcher of the Spheres, Empyrean EagleEmpyrean Eagle, and Warden of Evos IsleWarden of Evos Isle that care about creatures with flying
You sit there wondering if your tablemates know how close they are to losing and whether they'll have the answers they need in order to stop you
The bigger question is still probably how to get it into Modern without ruining Standard for two years
In the end, regeneration is about preventing your creature from destruction
Its also important to note that some older sets didnt have foiling since WotC only started printing foil cards in Februrary 1999 with Urzas Legacy