On my "last turn" in the second game, I used a shotgun instead of a grenade - it was a mistake, but I did not deal any damage and it did not affect the game much, but by the harsh rules, I lost instantly.
Sibi, it is simple, if you want to gain weaponretreat time cuz your turntime is about to end, and you're going with the Grenade worm, throw a grenade and there you go.
It's not hard. And don't shoot with shotgun, cuz its cow as it is stated in the cup, it's quite simple. And remember your weapons. Even if you forget, press "delete" button 3 times, and the nametag of the worm will reappear. These are all written in the cup description. The rules speak for themselves, if there was a solution in WA that we could disable every weapon and that in a Grenade worm's inventory there is only grenade and nothing else, we would do it. But there is no option sadly, so we maintain these basic rules.