Here are ability changes I think marci needs to make her more of a hard carry and less of a offlaner. First, we should keep her primary stat str but reduce her strength gain to 3 and increase her agi gain to 2.6.

her first skill needs to be turned into a 30% slow with Armor Reduction at 2/3/4/5 and the damage should be 125/150/175/200. (Magical) Removing the stun will prevent so many set ups under tower and obviously nerf this skill. Thats why the armor reduction is added so marci can at least do a good amount of damage early game. Her lock down ability is just taken away now.

Her second skill should be a dash with a distance of 700. This dash will have a 0.5s delay and marci will begin to glow (like her ulti) before she dashes forward. If marci doesnt hit anything, a 40% slow is applied for 4s. If she hits a hero, she will deal a 1.5s stun and gain an attack speed buff for 2s. Attack speed bonus 30/40/50/60. Damage (physical) 100/150/200/250 This will make locking heroes down more difficult for marci due to the cast delay. However, if paired with a good support, she can take advantage of that dash skill and deal a good amount of damage with the armor reduction from the first skill. I feel she will be able to scale better in the late game with the second skill as well.

Swap some aspects of her ulti and third skill.

Third skill. Every 4th attack Marci applies pulse to the target. (Similar to monkey Kings Jingu however you can work on creep/stacks.) Pulse will apply 20% slow and reduce attack speed by 50 for 1s. It will deal physical damage in a 500 radius but only apply debuffs on the target. Damage 40/60/80/100. This will allow her to keep up with other carries when it comes to farming. It might seem broken at first but keep in mind that specters desolate does 60 PURE damage on every attack if the target is alone. A 1 second 20% slow is not drastic either until you reach late game when marci gets her items or echo saber lol

Ulti: Marci’s ult will remain the same without the pulse affect. Only difference is all fury attacks are limited to 4 instead of 3/4/5. Marci will gain life steal, movement speed, and bonus damage. Lifesteal: 20%/30%/40% Bonus damage: 20%/30%/40% Movement speed bonus: 15% Duration: 16s/18s/20s