It's an 8 foot long (2.4 meter) spear-like weapon but with a thick wooden scimitar-like blade on one end. The wooden blade is coated in the strongest metal that can be found (tungsten) and sharpened on both sides of the blade. On the other end of the staff is a spiked metal counterweight that makes the weapon perfectly balanced in the center of the staff. It is usually used for cavalry attacks but is handy for ground combat as well. I think that this would be a hard weapon to master and that it would be fairly effective but I wanted a second opinion.
Ok. I think we should take this point by point.
1. 8 foot long (2.4 meter) spear-like weapon
Ok. There have been plenty of such weapons historically. This sounds fine. I should ask though. When you say 8 foot long, is that the shaft alone or does it count the head? Both designs exist historically, but which one you're going with would affect the rest of the evaluation. (I'll bring this up again when I get to the parts where it matters.)
2. scimitar-like blade on one end. (I decided to skip the wooden part down to #3).
Right. Let me stop you here. A scimitar curves WAY too much to take the directional stresses put on it by the extra torque of being handled as a pole-weapon. There are some scimitars out there that are curved at a level that's a little closer to a naginata, but if that's your justification then you might as well just call it a naginata.
3. The wooden blade is coated in the strongest metal that can be found (tungsten).
Now THIS one is tough. In fact, it's probably the largest point of difficulty on here.
1st off, Tungsten is actually HORRIBLE for use in weapon making specifically BECAUSE of how hard it is. Hard = will keep an edge better, but it's more brittle. In other words, tungsten will chip and break very easily due to it's lack of bendability.
The tough part here is the idea of it having a wooden core. A core made out of a softer material that has quite a bit of bend and give to it actually is a common technique used to counter-act the downsides of a brittle hard material. I'm really not sure wood is going to cut it though. It might be going a little too far in the other direction.
Yes, live green wood does bend. However, dead wood becomes brittle as well and breaks way too easily. And, as covered, the tungsten would also be brittle.
I would say this could work if you make the core of the blade out of steel or wrought-iron. (Iron with a carbon content lower than steel. It is soft, but also very bendy. Iron with a carbon content higher than steel is called cast iron, and it's hard and brittle. Steel is actually the term we give to iron that has it's carbon in that goldilocks zone where it's neither too hard or too soft.)
4. On the other end of the staff is a spiked metal counterweight that makes the weapon perfectly balanced in the center of the staff.
Ok. If it needs the counter-weight, I'm going to presume you really meant it when you said the blade was thick.
In terms of weapon performance, I would say it can still function effectively in combat. However, this does bring up one potential problem. How strong is the person wielding this weapon?
If you're talking a spear with a counter-weight, then that means it's definitely quite heavy. This will cause it to tire out the muscles of the person wielding it, making it unsuitable for long periods of combat. So, it won't really be usable for your common infantry or cavalry man.
However, if you're talking the spear-toting equivalent of the English longbowman (the hardest part about training archers is getting their arm and back strength up), then it's perfectly fine. Skeletons have been found in Europe and other areas where lances were used where their right arm was noticeably larger than the left, even with the skeletal remains. These career lancers would have likely been able to carry this weapon you're describing no problem.
5. It is usually used for cavalry attacks but is handy for ground combat as well.
Alright. Here's where we have our potential problems cropping up.
Exactly what kind of ground combat are we envisioning here? The weapon you described would function perfectly well on horseback, but I can see some problems in ground combat.
Because you described the counter-weight as being spiked before, I am guessing you meant for it to be used in a one-on-many combat situation? Well, I don't think you need me to tell you this really isn't how combat went historically. But, having two threatening edges to it like this probably could be useful in warding off a large number of enemies if you get knocked off your horse during a cavalry charge and need to ward people away for a moment so you can make a break for it and get back behind allied lines.
On the other end though, I'd be concerned about the spiked end harming the horse if you're using it primarily on horseback.
Also, this is the point where the 8 foot shaft Vs. 8 foot total length question comes into play. 8 foot is an alright length for a naginata in terms of total length, and would be considered perfectly balanced. However, if you're talking 8 foot shaft with a blade on top of that, then you are talking a weapon too long to be used in single ground combat.
Pole weapons of that length would commonly be used from the back ranks of pike charges, essentially pikemen with even longer pikes than the front rank would bring their pikes down between allied units in order to add more pointy sticks to the charge. It would be a weapon standardly used in group combat.
I think that this would be a hard weapon to master and that it would be fairly effective but I wanted a second opinion.
I don't hear anything outrageously bad about this thing, but the spiked counter-weight doesn't really strike me as something that would come of use in all that many realistic situations. Also, as mentioned, there's the very real risk of it injuring the horse. I do not see a weapon with that design as ever existing outside of a none-off novelty request, and with a disadvantage like that it would become quickly disfavored.
As I said, not outrageously bad, but that spiked counter-weight holds more disadvantages than it does advantages.
Also, the tungsten and wood thing is another point I don't really think entirely works out. You might want to see and consider my comments on that section.