(Nope, you read it right! Your move gives you 30 ft, then you have five dash actions. You can use one of them as a bonus action for your champion challenge. You have an attack you can use as well, but they are slightly out of range, meaning you'd need a ranged attack.)

Titus speeds across the rooftops alongside Rethan, matching the pace of the devils for the moment. As he begins to lose steam, he barks out his challenge.

Devil 1 WIS Save: 21

Devil 2 WIS Save: 8

Devil 3 WIS Save: 6

DM Shield:

Titus' steps are careful and surefooted, but his challenge goes unheeded. (If Titus wants to make a ranged attack against one of the devils, I will retroactively apply it.)

Laniel continues trying to catch up down on the street. He races down the same alley as Mal, finding him prone, and helps him up (Laniel's action), then continues his pursuit.

CON check: 3

DM Shield:

As Laniel sprints through the streets, a beggar steps out in front of him. Unthinking, Laniel shoves the poor man aside, pushing him roughly up against the wall. "I'm terribly sorry," Laniel says, as he continues the chase.

(Laniel is 20 feet behind the devils, although they go next. Also, he is two stories below them at street level.)

The lead spined devil screeches as it is struck by Rethan's first blow. It is clearly injured but persists in running. They seem to have a clear destination in mind and are determined to make it there.

DM Shield:

Each of the devils lets loose a spine.

Spine Attack against Laniel: 18 Damage: 6 (3 of which is fire damage)

Spine Attack against Titus: 17 Damage: 8 (3 of which is fire damage)

Spine Attack against Morph: 8 Damage: 7 (3 of which is fire damage)

The spined devils continue their flight (200 more feet)

DM Shield:

Disadvantage roll for Laniel's attacker: 13

Disadvantage roll for Morph's attacker: 16

Laniel and Morph and Titus all dodge their attacks. The spined devils' flight is without obstacle.

(Morph, Titus, Rethan, and Mal can go in any order.)

(How far behind is Mal at this point? I figure that with 8 dashes from last time, I should have covered 270 feet in a single turn. I am probably still about 250 feet behind though, near Laniel, right?)

(280 feet behind the devils. 60 feet behind Laniel now.)

Mal will pursue, dashing 6 times (210 ft closer) to close within 90ft of the devils. If successful, he will try to throw a sleep spell as an action all the way over to the clump of devils.

Con check:15

For the sleep spell: 23

Mal dashes through the streets, leading Laniel and keep pace with the spined devils. He lets a magical little song drift forth on the hot summer air and the lead devil flutters to the ground, asleep, but the other two remain aloft.

DM Shield:

 This time, Mal faces no obstacles on his pursuit. Mal is 70 feet behind the devils.

(Rethan, Titus, and Morph are next.)

(Just to confirm, is the lead devil the one Morph has been keeping an eye on, the one with the item? If Morph needs to make any rolls to have kept track of which is which, just let me know.)

Rethan continues to dash after the devils, striking out when he gets close enough. 

(6 dashes to move 210 feet so I can get melee range.  Con save: 6.  If the key carrier was not the one that was slept, throw a net at him)

Net Attack: 10

(Since they haven't been out of sight, it is apparent the sleeping devil is the one with the artifact. Rethan can edit or add to his actions if needed.)

(Would throwing the net over him to keep him there wake him up?  Doesn’t do any damage)

(Hmm...I'm going to say yes, unless it is laid on him like a blanket.)

(I'm not sure about how far behind Morph was, so let me know if I need to modify this)

Morph sees the target devil, descend towards the ground, and follows it.

Move: 50ft + 150 (from 3x dash)

Seeing the devil asleep, Morph tries to locate the item they have been trying to acquire, without touching the sleeping devil.

Investigation check to locate the item: 4   (Disadvantage for no touching? or should I be using Perception?)

IF Morph locates the item:

Morph, seeing the item, tries to get it off the devil without waking it.

Action: ??? (do I need to try rolling anything?)

IF Morph cannot locate the item:

Morph utters an arcane word and with a flick of his wrist, his eyes begin to glow a light blue again.

Action: Cast Detect Magic, dropping concentration on Silent Image

As the giant arrow above disappears, Morph checks again to try and find where the item is. (I assume Morph would know if the item was gone or still there at that point)

(Morph is 235 feet from the fallen devil. He will need to make a CON check to push up to 50 feet further. No check will be necessary to retrieve the artifact.)

Rethan hesitates for a moment, unsure what the best course would be, only to have Morph dart in ahead of him.

(I'll grab the item if morph doesn't)

(Go for it VanderLegion)

Morph flies down towards the downed devil, but is beaten to the chase by his friends.

Titus usues his five dashes to catch up with his friends who are standing around the sleeping devil. He sees they are focused on the artifact so he positions himself to shield them, ready to engage with the other two devils if they turn back.

Morph keeps pace with the devils but gains no ground on them. He is able to verify that the sleeping devil has it. Rethan dashes forward and must climb a stack of crates to get to the devil, which slows him down but not enough that he cannot grab the artifact from the it. In a bold follow-though, he swings his glaive at one of the devils still flying above them, following it with a jab of the weapon's butt.

Glaive Attack (against SD2): 24 Damage: 9

Glaive Butt Attack: 17 Damage: 5

Both strikes land, breaking the tough skin of the devil.

Then Titus closes in on Rethan and the devils, but has 20 feet remaining to reach them.

DM shield:

Laniel continues to race through the streets. He does not need to push himself any hard than he can handle and finds himself below the devils in the street. Laniel begins climbing a ladder, making it only halfway up by the time Rethan and the devils begin to tangle.

DM shield:

 The spined devils will not accept defeat easily. SD3 flies down and swats at Rethan's wrist to try and disarm him from the artifact using its devil fork.

Disarm attack: 22

Then it bites at him angrily.

Bite Attack: 12 Damage: 8

Both attacks are ineffectual, so the other devil attempts the same thing.

Disarm attack: 17

It then bites the sleeping devil to wake it up.

Bite Attack: 19 Damage: 5

The third devil awakens and screeches angrily at finding it no long has the stone. Rethan is now surrounded by 3 very upset spined devils.

(Rethan, Titus, Mal, and Morph may all have their turns in any order.)

Morph seeing what is happening, holds up his focus and points to Rethan.

To everyone else, it appears as if Morph is silently mouthing words, but Rethan hears what is said, as clear as if it was whispered in his ear.

Action: Cast Message at Rethan: