Gigantamax Gengar has low HP/defense, but it is difficult to stall when it got stronger. Practically, Fog weather would be required to Duo it without Max Mushroom. Although you can always try your luck and get a run where Gigantamax Gengar almost never use LARGE ATTACK.
Gigantamax Snorlax and Gigantamax Machamp Duo Battles will be posted in comment.
by Nikaidou_Shinku