a few more I've seen:
The thief with a 1 level wizard dip, using fast hand to cast true strike and attack as a bonus action, then holding their action to attack as a reaction, granting easy double sneak attack/round.
Another one I wouldn't allow. I'm not going to argue about it again.
Agathys Forever: I invented that one, although it is very possible that someone else also came up with it before me.
Basically, changes in the wording of the spell mean that you can now "recharge" Armor of Agathys, allowing you to inflict the cold damage far more often. At mid level, have the warlock cast it (as a level 4 slot) and then have the wizard change the warlock into a giant ape... you still inflict 20 cold damage to anyone who hits you, but you have 157 temp HP of good times until it expires. There are also a lot of other sources of temp HP that could be used.
I'm also rather... alarmed by the nick weapon mastery and how it's being interpreted. I thought that using a nick weapon meant that your bonus action didn't have to be used for the off-hand attack, meaning you could attack twice at low level and still have other things to do with your bonus action. Feels like it makes the fighting style finally balanced!
Instead, you can get two extra attacks if you do use your bonus action. That seems... not right.
I'd rule that you can't attack a second time with your off-hand weapon as a bonus action.
These kind of exploits have been brought up in every edition of the game. It's up the the DM and group to decide if they want to allow them. If you do, it just means as a DM I have to turn up the difficulty dial a bit. You can't "win" D&D through exploits, the DM can always counterbalance.