I'm looking at the Tavern Brawler Feat and realizing that it is likely going to drop in effectiveness as a character levels up and encounters more monsters resistant/immune to non-magical attacks.
Are there ways for a pure fighter to be able to make an improvised weapon attack magical for the means of bypassing resistance/immunity?
Best Answer
Get yourself an Infernal Banner
The description of the Battle Standard of Infernal Power (a very rare magic item) from the Baldur's Gate: Descent into Avernus adventure (p. 223) includes the following benefit:
So if you, or one of your allies, is holding the banner your weapon attacks count as magical, even the improvised weapon attack you make with an old frying pan or dead
goblinimp.Use magic items as your improvised weapon
From the Monster Manual section on "Vulnerabilities, Resistances, and Immunities" (p. 8; emphasis mine; note errata):
This doesn't require the magic item to be a weapon (normally), so if you hit someone with, say, a Broom of Flying, it is an improvised weapon attack and it is magical.
There is some disagreement whether the above works (see here and here at your own risk), arguing that magic items don't count as magical weapons when used as improvised weapons. This I agree with; however, the resistance is against nonmagical attacks and, by the above quote, an attack is magical when delivered by a magic item.
Regardless of the rules-quarreling, I need only imagine a burly fighter wail at a golem with a Broom of Flying to know that attacks delivered through the medium of an enchanted broom is in fact, magical (in more ways than one).