D&D 5E On Attunement and the Activation of Magic

[crazy_monkey]

It's only resistance, not immunity, so the fighter is not out of the fight. Sure, it sucks doing half damage, but that's still better than nothing.

Oh, that's a really good point. And resistant as opposed to immune make it terrifying without making is unbeatable. Nice.

Besides, if the party want the fighter to be fully effective, they have a solution easily available to them: have the fighter attune to the mace. If they choose not to do that, then they're also choosing not to let him be fully effective.

I was making the assumption that the party didn't have an hour between knowing they were facing an enemy with resistance to normal damage, and actually engaging. That is an assumption, though.