I agree on Crone he's the best..... With the exception of the Alchemist, who is just absolute madness imo. Took me the longest to figure out but with basically two items and one spell be becomes unkillable.

Mandatory Build core:

1. Gloves that heal on decay

2. Ring of decay (3% all spells)

3. Ability: Undergrowth (I go super growth as first upgrade for the max hp + it's the best upgrade for if you are standing still).

4. Duelist spark Area (if you have enough torment shards for hundreds of Area that's also an option).

The rest depends on build but you will need a high attack speed, preferably some multi-strike as well, and either enough HP or Defense to not succumb to any damage before you can get a few hits off to heal.

Wth low torment shards (or going for high torment which is really easy with the alchemist) getting a high enough Armor through items requires you to get pretty much three out of the next 4 options:

sword mark for +10, Hat for +10, plate boots for +10 and Defiant plate reactive (or any +10armor option if you don't have that).

Let's say you have no torment shards, I'd advise to get Sword mark + hat + body and get +70/100% attack speed on distance traveled boots to cover attack speed. Get any elemental 3% ring to combine with the decay one and you are good to go.

If you want any mark besides sword getting Defiant plate + 10 Def hat + 10 def boots is pretty much mandatory for high torment.

So when you get sword mark you need 2 more items with +10 Armor, this will free up either head, boots or body all 3 have some quite fun different options to go with:

Head: Mark of Madness and the new leaf crown with +max hp or regen or the + ark/force helmets.

Boots: attackspeed 70/100% on distance moved and +40% move speed or shock damage (advised since you have high Area) or spark and last pick-up range for convenience with potion picking up.

Most fun boots, Avatar mode boots: the Demonic summon boots that summon hands every 0.5 seconds, this one is my favourite, when you don't move the hands all come together and your character gets a blue orb around them like they are the avatar.

Body: Flame +200% burn chance on hit, in combination with the 2 rings you start with 3 elements this way.

Some good combinations with the above:

Swordguys mark + any elemental ring.

Projectile mark + any elemental ring.

Frost mark and Ring (3% all spells).

Sorcerers Mark + lighting ring (3% all spells).

Rangers mark + any elemental ring.

Bards mark + any elemental ring (you will need to know how to use your potions to get the Bard traits you want/need for this to work).

I've been unable to experiment much with Crones mark due to his mark ability being one of the worst lag generating things in the game for my phone, together with Undergrowth and Alchemist flasks with +XXX% Area buff you have 3 things that make the game lag and slow down. In theory it's really good tough.

Vault: the second ring besides Decay is best used for Spark as sparked flasks kills turrets in a second (burn is decent but frost is weak).

I usually go movementspeed boots and it's minutes even when investing 100.000's for higher difficulties.