According to Mark Rosewater on his Blogatog, it was discontinued for several reasons, including a lack of funding and a shift to prioritize other events
Dodging removal was a big part of why Copter was so powerful but these days it feels as if the card is fairly easy to take down, or at least compared to when the card was first out and so utterly rampant
Since this ability demands a diverse creature base, a Birthing Pod or creature-based strategy works great
Big Mother Mouser Dragon Broodmother Duskana, the Rage Mother Elesh Norn, Mother of Machines Faerie Guidemother Faerie Guidemother Grandmother Ravi Sengir Grandmother Sengir Hit the Mother Lode Hydaelyn, the Mothercrystal Ishkanah, Broodmother Mother Bear Mother Kangaroo Mother of Goons Mother of Runes Mothers Yamazaki (playtest) N'Yami-Class Mother Ship Phyrexian Vatmother Queen Mother Ramonda Rug of Smothering Sakiko, Mother of Summer Sliver Gravemother Sliver Queen, Brood Mother Smother Smothering Abomination Smothering Tithe The Goose Mother The Motherlode, Excavator Wort, the Raidmother
We have some other coin flip cards that aren't quite as good, but decent enough to be worth running