I mean, there's definitely a way to make the spear work but using a system that involves...

• A railgun
• Advanced materials science (low temperature magnetic ductile alloy)
• Electronics and moving parts inside the projectile
• Some high-wattage instantaneous heating equipment

... is going to be extremely complex and expensive. You'd need a significant power supply to power the railgun and the pre-heater, and this, along with the general size of this thing, would make it an exclusively vehicle mounted weapon. Additionally, building electronics into a munition, is difficult, and adding moving parts that need to function after being fired is quite challenging.

If you really want to come up with a new weapon to specifically deal with this beast, maybe a large taser could do the trick: since you already have the immense electrical power supply needed for the railgun, you could simply use two railguns or traditional guns to launch two inert spikes that trail long wires into the beast. Upon hitting and penetrating, the monster heals around the spikes and isn't majorly affected, until the power is turned on along the cables. This fries the nervous system of the beast and while it doesn't kill it outright, it knocks it out and disables the regeneration (which is controlled by the nervous system). Once this is done, people can approach with power tools to manually take the incapacitated monster apart. That said...

Despite how "un-sexy" traditional firearms might be, they would still probably deal with such a monster quite well. I mean, small arms might not do the trick, but if you were able to mount a big weapon on a vehicle you could easily turn anything biological that the gun can be aimed at into fine paste post-haste.

For example, take the GAU-8 Avenger: a hydraulically-driven seven-barrel autocannon capable of firing 30mm explosive shells. Each shell, containing a depleted-uranium penetration in the case of the armor-piercing variant, has the energy equivalent of around 50 grams of TNT. This is similar to the amount of high-explosive in a hand-grenade, so quite deadly but nothing obscene. Now consider that the cannon is capable of firing 3900 rounds per minute. No matter how fast the beast can regenerate, I don't think it would be able to survive this.

I mean, there's definitely a way to make the spear work but using a system that involves...

• A railgun
• Advanced materials science (low temperature magnetic ductile alloy)
• Electronics and moving parts inside the projectile
• Some high-wattage instantaneous heating equipment

... is going to be extremely complex and expensive. You'd need a significant power supply to power the railgun and the pre-heater, and this, along with the general size of this thing, would make it an exclusively vehicle mounted weapon. Additionally, building electronics into a munition, is difficult, and adding moving parts that need to function after being fired is quite challenging.

If you really want to come up with a new weapon to specifically deal with this beast, maybe a large taser could do the trick: since you already have the immense electrical power supply needed for the railgun, you could simply use two railguns or traditional guns to launch two inert spikes that trail long wires into the beast. Upon hitting and penetrating, the monster heals around the spikes and isn't majorly affected, until the power is turned on along the cables. This fries the nervous system of the beast and while it doesn't kill it outright, it knocks it out and disables the regeneration (which is controlled by the nervous system). Once this is done, people can approach with power tools to manually take the incapacitated monster apart. That said...

Despite how "un-sexy" traditional firearms might be, they would still probably deal with such a monster quite well. I mean, small arms might not do the trick, but if you were able to mount a big weapon on a vehicle you could easily turn anything biological that the gun can be aimed at into fine paste post-haste.

For example, take the GAU-8 Avenger: a hydraulically-driven seven-barrel autocannon capable of firing 30mm explosive shells. Each shell, containing a depleted-uranium penetrator in the case of the armor-piercing variant, has the energy equivalent of around 50 grams of TNT. This is similar to the amount of high-explosive in a hand-grenade, so quite deadly but nothing obscene. Now consider that the cannon is capable of firing 3900 rounds per minute. No matter how fast the beast can regenerate, I don't think it would be able to survive this.