Ok, so my current playgroup is in a bit of a pinch. They are a tad under-leveled, and are currently down two party members, because of real world stuff. So I nerf some of the enemies to help give them a leg up while they are short handed,( still making it a reasonable challenge of course, dont want to take the fun out of fighting) but even then, they are barely managing, mainly because they like to goof off and do outrageous shenanigans. Which I am perfectly fine with! It is super fun, and i dont want to make things dreadfully serious, so i am thinking of bringing in a character that is run by me to kind of be support. Like a Jace Beleren-ish wizard or bard, or just someone who heals and stuff. Just til the others are able to return. The last time i brought in a character was my Warlock, but he just ended up doing most the heavy hitting and was stealing the glory a bit, so i kinda want to avoid that again if I can. Any suggestions or helpful tips? Please and thank you.

Oh and the current party, minus the two gone, consists of a Goliath Berserker, a Tiefling ranger, a half-elf rogue, a human wizard, and an NPC knight named henry, who mostly serves as cannon fodder.

They should have sufficient damage output. Just be more rewarding in providing health potion/scrolls giving them enough ways to, for a bit cheaper then usual, heal up. I don't see a need to add another DMPC. Especially since you didn't have that good luck last time with it.

You know, I actually completely forgot about the concept the loot. XD 

But thats a pretty good idea, I think I will try that, and see how it goes. Thanks.

Loot is one way to solve the problem, but a follower character isn't a bad one, either, especially if the party is really suffering due to the absence of a role.  Be warned though; the addition of an NPC to the party is sure to entice shenanigans.  Players get REALLY... um... "creative", when it comes to how an NPC eventually ends up getting used.

Oh and the current party, minus the two gone, consists of a Goliath Berserker, a Tiefling ranger, a half-elf rogue, a human wizard, and an NPC knight named henry, who mostly serves as cannon fodder.

 You have a tanker, striker, trapper, and blaster. If you wanted to bring in a healer (straight Cleric or a healing-focused Bard), you should be good to go. Most of the modules are written for four to five characters. If they get killed because of their shenanigans, then it would more like their actions killing them than you.

You already have a bullet sponge in the NPC Knight, I don't see a reason for another NPC/DMPC to join the fray. As was pointed out; your group is fairly well put together even being down two. Using consumables as the fill in for a healer is probably the best course of action. I say this coming from a DM and Player perspective both.

DM Perspective: You've had issues with your npc/dmpc previously, why push your luck. You're teaching the players a new skill in resource management, and still allowing them freedom to be silly. This is a good thing for the DM as you will be able to run with players missing more often as they'll learn to survive without certain party members and still play true to their form.

Player Perspective: If I didn't have to worry so much about my role, I'd probably do even more silly things. I'm already playing a character who's crazy enough to leap off a 10 ft tall wall and drive a spear into a flaming horse, just to make it's owner really mad at me. Now, I have a dmpc, shoot, I'd just try to mount the horse and steal it..the dmpc can take care of my party. However, if all I had was an extra potion or three, I'd still have to play tactically but I can do so with a bit more flare since I can take that extra hit.

Alright, well thanks everyone. I suppose I'll attempt more resource management with healing and stuff and see how that all goes. Will update later and let everyone know how it worked out.

I would add a Cleric or Bard focused on support, possibly with a bit of tanking ability.

A Bard (or using Wish) could also enable a lot of ridiculous stuff to work, which would be pretty cool for the players as well. 

If shenanigans are causing them to almost lose, that's kinda their own fault, isn't it?  I suppose it depends what kind of game you're running, but at my table we run a serious campaign with lots of joking around.  Meaning, basically, you can say a lot of funny/stupid stuff but if you DO something stupid, the world will behave as it would.  Mortal enemies will capitalize on stupid stuff. We also have the "said it, did it" rule, so that cuts down on silliness feeding everyone else being silly, feeding, feeding, feeding. Also, if a character perma-dies, it tends to instil a sense of mortality and consequence, so they won't have died in vein.

If that silliness is what everyone is showing up for, then you wouldn't want to kill it, but if it's causing the DM problems, ask them to tone it down bc it's getting hard to balance.  Many times a simple conversation is best.  After all, if you can ask thousands of strangers for advice on it, you can probably ask your friends at the table to help you out.