Nice action economy. Also a save for half damage (does not miss!).

Good for creatures weak to fire, its a repeating source of fire damage for bonus action.

Just remember that it only does damage to a creature within 5 ft at the end of its turn, so the creature can avoid recurring damage by moving away during its turn. Only way to avoid that is to use your action to ram it into the creature. Still, good multi round attack for one spell slot.

Spellword is:

Rollarium Pyronus

Bonus action, not action. It’s when you ran it from moving it which moving it requires your bonus action. 

*bonus action to move sphere*

Big question: does it occupy a space? Can you block a 5' wide hallway with it? Can it occupy someone's space like an air elemental?

What if you ram someone into the sphere?  Such as with a shove or any other forced movement.

Although RAW states that only creatures can control spaces,  I would argue that, because the sphere takes up the entire square, because it is 5 feet in diameter, it would either block the space or at least cause the creature to make the save against it.

If you ram the flaming sphere into someone as the bonus action, and they make the save, do they still take half damage?

Just for point of clarity.  

 If you ram the sphere into a creature, that creature must make the saving throw against the sphere's damage, and the sphere stops moving this turn.

The spell dc stays the casters DC it doesnt become whatever the damage rolled. 

I.e, A caster with a spell DC of 15 used their bonus action to slam a monster.  it rolled an 8 for the 2d6 damage.  The save DC stays 15 correct?  It doesn't drop down to the 8 it rolled for damage.

Quote from kyle_the_wizard >>

Just for point of clarity.  

 If you ram the sphere into a creature, that creature must make the saving throw against the sphere's damage, and the sphere stops moving this turn.

The spell dc stays the casters DC it doesnt become whatever the damage rolled. 

I.e, A caster with a spell DC of 15 used their bonus action to slam a monster.  it rolled an 8 for the 2d6 damage.  The save DC stays 15 correct?  It doesn't drop down to the 8 it rolled for damage.

[Edit: meant to reply by quoting, forgot to do that.]

I was wondering this exactly (as I plan on using it in an upcoming encounter with some Flameskulls.)

My reading is this: in the spirit of "spells do exactly what they say, nothing more or less," I'm looking at "the saving throw against the sphere's damage" on a bonus action ramming as the same kind of saving throw against damage if they are within 5 feet of it at the end of their turn. Since the text says "Any creature that ends its turn within 5 feet of the sphere must make a Dexterity saving throw. The creature takes 2d6 fire damage on a failed save, or half as much damage on a successful one," I would read "the saving throw against the sphere's damage" as a save against the caster's DC.

If it said "must make a saving throw against the sphere's damage" then I would assume it would be a contested roll. 

So, a scenario: a caster with a spell save DC of 15 casts Flaming Sphere as an action. It doesn't do damage when cast. As a Bonus Action, the caster rams it into a PC. That PC has to make a Dex save against a 15 DC when they are hit. If a PC ends their turn within 5 feet of it, they make the same DC 15 Dex save.

Does that make sense?

It’s a bonus action to move it not an action.

If you were a celestial warlock, and you ram this into an enemy, would you add your charisma modifier to the fire damage because of celestial warlock's Radiant Soul ability?

Quote from Patrope >>

If you were a celestial warlock, and you ram this into an enemy, would you add your charisma modifier to the fire damage because of celestial warlock's Radiant Soul ability?

 Yep! It's not just limited to attack spells.

"when you cast a spell that deals radiant or fire damage, you can add your Charisma modifier to one radiant or fire damage roll of that spell against one of its targets."

For a celestial warlock, this seems better than hunger of hadar.

> When you move the sphere, you can direct it over barriers up to 5 feet tall and jump it across pits up to 10 feet wide. 

Does this mean that the sphere rests on the ground and can only move as if rolling? The fact that it appears in an empty space of choice would mean everywhere.

But it said if you ram into a creature they take damage too, even if its not the end of their turn

Some reason this hasn't been added to the sorcerer's spells after Tasha's. 

Which I am still under the impression that Crawford hates Sorcerers. Besides being underwhelming in the PHB with not expanded list for the subclasses, almost none of damage spells can be twinned via his rulings. 

Virtually no bonus actions unless you go divine soul. Or waste a ton of resources to add a cantrip worth of damage. This spell should have been a sorcerer's spell from the beginning IMO. 

This is listed on the "Sorcerer" class page, I have bought all content, yet why does it not show up as a spell to choose for my char? Is there something on my char that would restrict this?

https://www.dndbeyond.com/classes/sorcerer#OptionalClassFeatures 

Additional Sorcerer Spells

Edit:
Found it, I didn't know this until now but it IS a way you can set up your char...