I like the concept of cursed equipment and wished we had more of them. They are usually better compared to their equals, but come with drawbacks you have to work around. The Light of Creation surely is a badass piece of equipment: It is a +1 magic weapon at a point where good weapons are rare, has a DR, and has Extra Reach and Cleave on top of that. However, on every strike there is a chance you get stunned, which would be awful and will happen at the most inopportune of times. It does not apply to constructs and the wiki recommends the Gloves of the Automaton, which would turn you into into a construct. That piece of advice is not very good though; the gloves are only available a bit into Act 2, at which point you have competing options without drawbacks like the Unseen Menace or the Halberd of Vigilance, and they also occupy the coveted hand slot. We can do better.

Every strike you need to succeed a DC 10 CON save. That is actually pretty achievable with just some minor accommodations. The goal is to use the weapon between Level 5 to 8, because the biggest perk of this weapon is its availability. You can push Bernard off the tower with Thunderwave or Repelling Blast while the rest of your party waits at the bottom. He will not quite die from the fall, so your party better be in turn-based mode to prevent him from getting up and heal himself. Anyway, his weapon is technically accessible without having to property fight anything beyond the grove battle, which can not be said about the Mourning Frost - and you might want to delay receiving the powerful, but temporary and only one-time Bliss Spores buff until you wrap up more important checks.

Fighter/Barbarian

CON Bonus at Level 5

Fighter or Tiger Heart Barbarian derive the most value out of a powerful weapon due to being able to attack the most targets via Action Surge or Tiger's Bloodlust. They also happen to come with CON proficiency, which makes things a lot easier. In the same vein, a Human or Half-Elf Sorcerer would also be able to wield it. A more martially oriented Blue Draconic Sorcerer might even have some fun with Lightning type Booming Blade. Just note, that they rely a bit on Hill Giant elixir until they can dip Hexblade at Level 6 or 7.

The sources of CON saving throw bonuses are following:

• +3 Proficiency
• +3 CON modifier
• +1 Helmet
• +1 Ring of Protection

Start with 17/15/16 STR/DEX/CON. The 15 DEX is not actually redundant, because on an Initiative tie, the higher DEX wins. There are a lot of 14 DEX enemies that 15 DEX allows you to jump over, like a good bunch of goblin types.

The Ring of Protection is assumed to be available. You can steal the idol relatively early if you are careful, but you usually confront the Shadow Druids at Level 4, so it is assumed to be within the bounds.

That's +8 right there. You always roll at least a 1, and the DC check does not fail on a natural 1, so any other source of a +1 will guarantee imperviousness against the backlash. Those are:

• Be Astarion, Be Happy
• Bless (or The Whispering Promise)
• Warding Bond
• Resistance cantrip (takes Cleric or Druid concentration)
• Bliss Spores (one-time, not repeatable)

Use two of them if you have 14 or 15 CON.

You could hypothetically also spend a feat to gain the remaining +1, but that one is to be avoided, since the ones wielding it really want Great Weapon Master or Savage Attacker instead. For the same reason we'd avoid picking Resilient CON with another class.

Fighter or Barbarian Astarion have the least trouble wielding it, because the Happy status is until Long Rest has no upkeep or downsides. The Whispering Promise at that stage of the game is likely best on the wielder itself in order to save spell slots and is also generically available. Warding Bond does require a Cleric, but is the most hands-off method aside from the Happy status. If your Cleric or Druid is not that reliant on concentration (yet), you can also cast Resistance before an encounter.

Other Options

While Fighter and Barbarian are the ones who get the most mileage out of this weapon, there are a few more niche builds. They all have in common that they need to be at least Level 6 to safely wield it, which is around the time you deal with the Grymforge.

GWM War Cleric

One way to play an early game War Cleric is with GWM and Cleave as a Short Rest nuke to milk Guided Strike for all its value. They are not Level 6 yet and can't pass the +10 Attack to other characters, but Guided Strike applies to their own attacks, and coincidentally, this weapon happens to be a halberd, an Extra Reach weapon with Cleave. 1 Sorcerer 4 Cleric would allow you to do that at Level 5, same time as the Fighter or Barbarian. As a personal preference, I usually play them as 2 Sorcerer 3 Cleric to leverage twinned Magic Weapon - by itself a questionable use of your concentration, but is more interesting when done on two weapons at the same time. They can still safely wield the Light (assuming Astarion or just casting Bless/Resistance), but GWM just comes a bit later.

I also usually play 2 Sorcerer 4 Cleric with Level 6 Sharpshooter, because Level 6 is the point where Arrows of Many Targets become available and upkeeping twinned Magic Weapon when ranged. The caveat I am getting at is that in a party where a Sorcerer War Cleric is present, the Light of Creation is rarely their weapon; they are there to enhance it, the Titanstring, or the Githyanki Greatsword for two dedicated GWM or Sharpshooter damage carries. Also, twinned Healing Word with Whispering Promise for concentration-less Bless.

Magic Weapon + Elemental Weapon

Paladin/Sorcadin

Whether a Level 6 Paladin activates Aura of Protection to compensate for the lack of proficiency or start as a Sorcerer for CON proficiency, they both come online at Level 6. The catch is that they come with no STR unless you entirely dump DEX. If you can hang on one more Level, you will be able to add a Hexblade dip to make it scale with CHA, which at that point of the game should take about 2 or 3 Elixir of Hill Giant Strength if you pace it generously.

If your Paladin increases CHA with the hag's hair, they will have +4 from the aura, which is equal to +3 proficiency and one of the requisite +1s.

PAM Tempest Cleric

A Tempest Cleric has the combo of Sleet Storm and Thunderbolt Strike on a weapon attack to knock back approaching enemies that save against the ice. That combo comes online at Level 6 at the earliest, when Thunderbolt Strike unlocks. They will pick Polearm Master as their feat, so there is no means of gaining CON proficiency on their own. What they can do is pairing up with a Paladin and their Aura of Protection, or a Transmutation Wizard and their Transmuter's Stone. Either of them will grant you enough CON saving throw bonuses.

Just like the Paladin, they will not come with enough STR by default. Unlike them, they do not have an equivalent of a Hexblade dip, at least not for this weapon. The preferred one is the Cacophony, on which they can apply Shillelagh in order to scale with WIS. The upside of the Light of Creation (Extra Reach aside) is mainly availability; it can be obtained without having to resolve the grove raid.

As of Patch 8, it should also be noted that the niche of having a Lightning or Thunder weapon with team mate support is diminished. Running a Hexblade Tome Warlock, whose main draw aside from Eldritch Blast (with Repelling Blast synergy) and summoning minions is to permanently concentrate on Elemental Weapon solves that set of problems all on its own independently from the weapon. Just cast Elemental Weapon on the Returning Pike, Monster Slayer Glaive, or Melf's First Staff and be done.