I'm not a passionate solo player, but there are some tips you might like to look at:
Use heroes with low BAT(Base Attack Time) value:
Juggernaut, Huskar(with enough armor, his Q can make him invulnerable to tower damage), Anti-Mage, Lone Druid(in bear form), Terrorblade, Troll Warlord(with Q set to melee).
Why would you need low BAT?
Because its your starting attack speed delay(or time between attacks). Also, heroes with lower BAT benefit higher even from slight attack speed buffs.

With low BAT heroes you can focus more on damage and cleave\split shot items, rather than balancing between attack speed and damage.

LC and Batrider(with orb of venom) are also highly sustainable, tbh.

Most spellcasters can provide alot of survivability, but only if you focus on mana regeneration items.

Hey and thanks for the reply!

I am aware of BAT and its mechanic/impact and values! :-)
Alche would be on that list too, as he has nearly perma ult with octarine and his ult lowers BAT aswell.
As far as i am concerned, spellcaster will have a hard time winning this, as most of them cant focus towers down quick enough and they also will have huge problems if certain bosses appear. (Especially the mana burn boss)
I think in solo, you have to win before Skeleton-Boss, as he will a) own most Heroes, even when they are 6 slotted and b) you cant reliably push since the mobs get so strong, that they will tear your base apart way to fast if you make a small mistake!

Ideas for Heroes that can solo?
Huskar, Doom, Alche, Morph, Drow, Dusa are the ones that come to my mind.
I didnt have a lot of succes with melees that dont have a good form of sustain so far, as it feels nearly impossible for certain boss timings, like the Ogre to kill the boss without the ability to kite that ranged heroes have!

Whats the highest difficulty anyone here has managed to solo?

Phantom Lancer is also a very strong hero. After heart, your illusions will help ypu a ton. The problem in solo is that the skeleton requires a few key items to be killed ( Shiva+, Heart, ecc. ) which sinergyze with only certain heroes. Also, after skeleton, the ice cream ancient apparitions will prevent you from soloing any longer since you can't both kill them and defend from the infinite bosses.
Solo mode should be a separate thing. 2p is made for 2 players, one focuses on those necessary auras and the other focuses on stats, damage, ecc. A great duo would be Pugna + Lycan.
Also, i think that melee carries are superior on solo, being able to benefit more from certain items.

I won solo using Centaur. I rushed heart on him, got some solar crests, boots of travel 3 and heaven's halberd.

During this run, I gradually upgraded my mid tower to level 10 to let it defend while I push mid. You will also have to gradually clear out the kobold camp for gold too, letting it stack too much without getting gold from it will cause you to lose easily. When bosses appear try to tank/kite it while your upgraded tower take it down.

Once you push down the tower in front of the barracks you can just skip the barracks and start on taking down the towers around the dire ancient. The return passive along with the str gain from heart/halberd, armor and evasion stacks of solar crest and halberd will make short work of these towers. if you die at any point, don't buyback unless absolutely necessary, your tower can hold on its own really well against mobs. I won at the 28 minutes mark just as the Demonomicon boss was making its way towards the upgraded tower.

I'm so rekt, why won't uoy just create a solo mode, I like this custom but its impossible to play it solo on every hero

Originally posted by QwernerVI:

I'm so rekt, why won't uoy just create a solo mode, I like this custom but its impossible to play it solo on every hero

It should not be possible to solo with every hero, just like in normal dota it isn't possible to carry with every hero.

Originally posted by QwernerVI:

I'm so rekt, why won't uoy just create a solo mode, I like this custom but its impossible to play it solo on every hero

Originally posted by SymphonicMetal:

It should not be possible to solo with every hero, just like in normal dota it isn't possible to carry with every hero.

Because of a bug, 2p map produces the same amout of creeps as in 4p\5p. With recent fix, it should become less tense, thus more doable.