Spending a ludicrous investment to an already ludicrously expensive weapon results in... What I would consider to be the strongest and most enjoyable hammer melee weapon I have in my arsenal so far, rivaling that to the Arca Titron.

This Sibear build won't be just for novelty - this is a very strong hammer that can hold it's own weight, even without Naramon. If it was a man it would make Frost fluster at the sight of it, and Frost already has a decently built body.

Pros:

• Guaranteed orange crits (and also red crits)
• Guaranteed statuses
• +480% potential added damage thanks to innate IPS and Cold statuses
• Fast attack speed
• Very quick combo buildup (max combo in under 25 seconds with Crushing Ruin on a single target)
• 11 seconds of combo duration
• High Riven disposition

Cons:

• Say goodbye to your Cryotics and Alloy Plates
• It's not [Glaive Prime] I guess 🤷‍♀️

This build ain't for your normal joes. What you put into a man is what you get. And this hubby won't disappoint.

Evolution Paths

2nd Evolution

• Master's Shatter is what makes handling this hammer feel not like hauling concrete weight, but holding the hand of the man of your dreams. It doesn't take several swings before the two of you start twirling around unfortunate onlookers that get in the way of your passion.

  I find the amount of utility this perk gives outweights the added damage of Thane's Wrath. Being able to build combo this quickly is a luxury especially to slow weapons such as hammers.
  If building combo isn't a concern for you, and you have armor thicker than that of Frost's, more base damage will go a long way.

3rd Evolution

• Resolute Force is the default go-to. With this you can maintain the intensity between the two of you for longer, as you make your way from one living bowling pins to the next.
• Orokin Reach would make for a good alternative, if you have other means of maintaining your combo.

4th Evolution

• Not much to say here. Use Absolute Valor as Master's Shatter does the job of Mounting Avalanche better, and turns what would be a mediocre status hammer into a critical beast. Maybe the bit here is that the Sibear works out at the local gym or something.

Notes:

• Here's a tip on getting Berserker Fury stacked quickly against heavies: do a neutral combo, and the final attack will perform a slam that knocks down enemies. You can then perform a ground finisher that will often kill heavies outright, stacking up [Berserker Fury] and allowing you to build combo proper.

Despite what the Incarnon description says, various slam attacks (including ground finishers) from stances will also spawn the Incarnon's slowdown field, keeping enemies already grounded for longer and nearby enemies.
Slam attacks will also only proc elemental status effects (not IPS statuses), which also makes for a good opener. The slowing field itself doesn't proc Cold statuses, however.

• Use Crushing Ruin's Shattered Village (forward + block) combo to build combo and statuses as it hits multiple times. You can switch to a different combo after the third swing to cancel the combo's final ragdolling slam.

• Use Tennokai as often as you can, as performing heavy attacks gives it +50% status chance for the heavy attack and any attacks during the following four seconds after.

  Heavy attacks also procs the Lifted status, scaling with combo tier up to 12 seconds, and also counting as a separate status for Condition Overload.

Viral?

You can run Viral and still be able to proc Cold to build combo off of. Though you will be restricted to radial slam attacks from combos and airborne slam attacks to be able to proc them.
As the damage of [Sibear] comes mostly from heavy attacks and doesn't have much Slash or Heat to speak of, I find that it benefits more with the added direct damage from Corrosive, especially when enemy armor becomes more a concern.
But if armor isn't a concern and you don't mind slamming every now and then, then you can run a Viral setup by replacing Voltaic Strike with Gladiator Might to get more mileage.

Mod options

• Primed Reach can be swapped for Sacrificial Steel for guaranteed red crits on basic attacks, and guaranteeing tier 5 crits on Heavy attacks with Melee Animosity compared to... tier 3 crits (reds). You'll need an additional Forma to do this.

  You still have Opportunity's Reach for the added 3 meters of your heavy attack, just not on normal attacks to spread statuses or build combo with.

• Opportunity's Reach can be swapped for Discipline's Merit or other Tennokai mods, if you want to make use of [Sibear]'s +50% status chance fully, or using Melee Duplicate in place of Melee Animosity.

• You can swap Voltaic Strike for Focus Energy if you're not running Tennokai mods.

Riven Recommendations

Replace either range or crit damage from this setup. Not much room to play with (or perhaps even to improve on!)
This [Sibear] does so much by itself that I imagine it could be hard to find a good riven combination just from the virtue of how good it is by itself. Your best bet would be attack speed, status chance, combo count/duration, or more crit damage.