The spike that Side B does is mostly useless, considering that his new Aerial Down B has the same speed, has a more reliable hitbox, and has a much stronger spike attached to it.
Out of all of the Side B moves, I feel as though the custom 2 variant is the most useful. It doesn't plant opponents in the ground as long, but it has these additional benefits:
- Does as much shield damage as the normal version
- You can dodge attacks with this, and the headbutt will come down and bury the opponent
- Becomes an interesting OoS Option
- Allows you to stall in the air, which allows you to bait Usmashes, Utilts, some aerials, and etc
- Falls incredibly fast, which can let you return to the stage really quickly (though it has punishable lag afterwards)
- You can also quickly snap to the ledges using the above method, making this a safer option to return to the stage
- Knocks aerial opponents away and diagonally upwards when it hits them, giving you a chance to chase/intercept them
- Does 10 damage, meaning that it is still pretty solid even if it trades
The only real problem with it is that opponents can pretty much immediately break out of the grounded effect it causes, even though opponents can break out of the normal variant pretty fast anyways. Still, I choose custom 2 over the default due to it having much more versatility, and its primary function of breaking shields is still just as effective. It's probably even more effective than the default due to the other benefits I mentioned above.
If you're not playing locally or with a friend though, the only time you would ever want to use Side B is when you want to break someone's shield, and that is very situational at best. Otherwise you shouldn't really bother with it, as DK usually has better things that he can do and not get punished.