Hello there,

As per Wiki:

• Tenet Ferrox: Upgrades to critical, status, fire rate, magazine, and explosion radius at the expense of damage; holding down fire button immediately charges the next shot.
• The weapon's max rank caps at 40 after 5 polarizations - max rank increases by 2 per Forma added (similarly as the Paracesis).
• All Tenet weapons deal innate elemental damage in addition to physical damage. The amount of this damage is random, ranging from 25-60%, while the type of element is randomly generated in Ergo Glast's shop, which are cycled every 4 days. Can be bought from Ergo Glast of The Perrin Sequence in any Relay for 40 Corrupted Holokeys.

According to the above, I added exactly 5 forma to this weapon, so we can obtain Mastery Points from it.

In this case, I recommend picking Toxin as an elemental.

Some info about weapon:

• This weapon deals primarily Puncture damage on its primary fire and Impact damage on its alt-fire
• Primary Fire charges and shoots thin beams
• Holding the fire button after shooting will immediately charge up the next shot
• Beams are hitscan and do not have projectile travel time, despite the animation
• Shots explode in a 4-meter radius after reaching maximum punch through distance
• Initial hit and explosion apply status separately
• Explosion does not need direct line of sight to deal damage and will penetrate walls
• Can benefit from Cautious Shot
• Vaporizes enemies on kill, making it good for stealth when silenced
• Alternate Fire throws the [Ferrox], creating a field dealing Electricity damage and pulling enemies within 10 meters toward the Ferrox every 2 seconds
• Throwing the spear consumes 1 ammo, then reloads the weapon
• The field lasts for 10 seconds
• Only one spear can be deployed at a time. Throwing the spear again will remove existing spears
• Reloads 33% of the magazine per second while deployed or holstered
• The Ferrox' alt-fire is affected by fire rate mods, making it tick more often

Enjoy!
THeMooN85