Oh I so wish “Siege mode” was still an ability and not a trait. (It wouldn’t do anything, but it also used to cost mana. So you couldn’t even activate an ability that does nothing)
I could switch it for “Cheap shot” bit I’ll keep what I originally submitted. for fairness.
So yes, you can only auto attack and press Z the entire game as a non global abathur. (and there are barely any talents existing in the game to increase the benefits here)
Body: Baby D.Va
Basic Attack: Probius
Q: Tracer’s Blink
W: Warp
E: Zeratul’s Blink
R1: Stage Dive
R2: Metamorphasis
Trait: Cybernetic Agility
Mount: Wall Ride
Man, and you though Tracer was mobile.
rexxar without misha
abathur, his abilities are no longer global, and must be used at melee range
varian, but he doesn’t get his lvl 4 talent
Whitemane post rework.
Trait: heal for damage
Q : Costs up to 150 mana
W Cost 80
e cost too much.
It’s garbage because if you use her spells instead of attacking you heal less while wasting mana for potential Qs
Dehaka without essence is more or less 60% of a hero, fun fact.
But how bout abathur without symbiote.
Name: UBU (useless but unkillable)
Body: Genji
Basic Attack:Probius
Trait: Undying
Q: Deflect
W: Safety Bubble
E: Dimensional Shift
R1: Taz’dingo
R2: Army of the Dead
Name: Probius
cries
K
Perfect!
“You asked for it”
Body: D.va
Trait: Zuljin’s Berserker
Q: Gift of Life
W: Blade Dash
E: Deadly Reach
R: Might of the Nerazim
I did one useless now I’m going to make the most Trollish hero:
The Lost Viking’s 3 Bodies
Trait: Tyrael’s Archangel’s Wrath
Z: Medivh’s Raven Form
Q: Baneling Barrage
W: Flame Strike
E: Plague of Toads
R: Play Again
Is that a snow shovel!? 
Hahahaha, I forgot about that one, thanks!
• Body: Murky
• Basic attack: Probius
• Trait: Master of the Cold Dark
• Q: Soul Rip
• W: Crippling Spores
• E: Eviscerate
• R1: Pylon Overcharge
• R2: Illusion Master
Better than any concept I come up with 
I once had a dream and i woke up almost crying,
that kind of dream you wake up and a huge wave of relief washes over you!
i dreamt that they actually made another “Nexus Hero” (but that was before Qhira and before there was that whole debate).
the problem was:
it was literally a test dummy from the practice range.
it looked a little different, in that its body was made up of springs instead of a strawman. but the shape and size and basically the function was similar.
it was as flimsy as murky or abathur, had no auto-attacks, its trait was that it deals back any damage like wobuffet, and its only!! ability was that it could do a cool spinning jump that didnt reach as far as li-mings teleport and did nothing else.
and i was so SO disappointed and legitimately sad and i wanted to cry.
On the bright side it wouldn’t be totally useless. The test dummy is quite tanky and can take a hit and if it deals damage back, now that’s op x)
And it has the “spin to win!”, there is no need for other abilities 
Hmm… Here’s a thought:
Body: Stitches
Basic Attack: Tassadar (Slow is listed as part of the trait)
Trait: Devotion
Z: Phase Shift
Q: Vindication
W: Butcher’s Brand
E: Deadly Reach
R1: Might of the Nerazim
R2: Adaptation
The result is that they get Uther’s 25 armor near constantly, with a continuous stream of healing on a massive body. 120 health per second with a range-8 160 DPS attack while Deadly Reach is up and the target has a Brand (with Brand duration actually being nearly perpetual), and 25 armor throughout that and the largest health pool in the game.
Unkillable, enormous range, but not much damage. Their only damage is the auto attack, though the E buffs that to a useful level. They do have a healing global, though, so they can save one ally on occasion with a pretty good burst heal.