The basic strategy only requires techies and then 4 other heroes that can get you to the end boss on level 15. Doing this is easiest with a lot of money on wave 10 and this guides the rest of the hero picks.
First is the strategy, second the hero builds including skill order and recommended items. Last is some tips I thought of and didn't fit in somewhere above.
Round one up to and including round 6:
Put Leshrac top left and let him handle it solo for as long as possible.
Techies on the spot below that.
Share the last two spawns with Axe, Medusa and Disruptor.
For wave 7 axe will need to rotate to help out and so might others depending on where stuff spawns. If things go badly rotations might be forced before this or could make things faster if they happened. Use your own judgement.
For wave 8 you want to group up Leshrac, Medusa and Techies to handle the two left spawns. Leaving Axe to handle the bottommost left one and Disruptor using wards to glimpse enemy groups in the bottom right as they spawn. This glimpse will teleport the enemy to the left side where you have three heroes waiting.
For wave 9 axe should move to help and Disruptor glimpse both spawns to them using his ward vision. If something slips due to cooldowns then Techies can help out.
Wave 11-12 keep up a split, letting Leshrac take the bottom right and Disruptor glimpsing the bottommost left spawns. If things are going well Techies should now be mining his spot from now on until the final Invoker spawns. If needed he can leave and help out.
Wave 13 group up and kill them one by one. Disruptor should kite them so you face at most 2 at once with the others in case you have a low killing speed.
Wave 14 is back to a split and hope nobody dies.
Wave Specific Information
Wave 9 the catapults spawn infinite amounts of small creeps. You need to kill them as soon as possible or be overrun. Reviving is hard since the catapult shots knock you back and deal heavy damage, avoid the circles. They can not fire near themselves so sticking close is a good way to avoid damage if soloing a side.
Wave 10 is hard to do right but matters a lot since it gives as much money as all the waves up until it. The idea is to use Axe call and Disruptor Kinetic field to lock the chickens in place while you use all your AoE on them. It is why Medusa goes early manta and why you buy and sell a refresher on Disruptor on this wave. The image below has a good position for this.
+ Show Spoiler [Image] +
As people are using skills they collect gold, excluding medusa that should always be attacking so maelstrom procs.
If you are not going for the techies mine solution to Invoker I strongly recommend pausing after this wave to discuss items so you get 2-3 Bloodthorns, Desolator, Assault Cuirass and Solar Crest on somebody.
Wave 14 kite things and dodge the jumping techies, they have a red circle showing where they will land. Keep running and they will miss, if you stand still you can't dodge them. Slowly kite them down and expect somebody to mess up and die. It is hard. Medusa might manage to straight up kill them if not too many spawn near her.
Wave 15 group up as 5 and kill the small invokers one by one. Make sure to use all active items to improve DPS. Make sure you have 120 or so mines at one spot while all 5 heroes avoid the invoker. Then put 4 heroes at the techies mines and kite with somebody to bring invoker to you by his self teleport. Don't forget to veil and etheral him for the bonus damage.
How to place the mines using aether lens:
Second before Invoker dies:
Disruptor is picked for his kinetic field that blocks in the chickens that give money. In coordinated runs the glimpse that bugs enemies to a spot on the left side of the map so other heroes don't need to move.
(If 5-stack buy wards to spot waves.)
Brown Boots - Save - Clarity
Orchid (if it goes very well bloodthorn but need Aghs at level 10)
Refresher during wave 10 for another ulti, sell so you don't lose money.
Arcane (disassemble and sell Energy Booster) -> Boots of Travels
Bloodthorn if you have enough for buyback and it.
Be flexible on your items, except for bloodthorn there is no item you have to have past wave 10.
If you glimpse an enemy that has not been alive longer than 8s it is moved to the left side of the map between the two leftmost towers on the left lowground. In organised play this can be used to speed up waves since 4 people can stand there waiting and take the left two paths at the same time.
Kinetic Field blocks the chickens on level 10 and should thus be used to be able to do DoTs on them to get a lot of money.
Your first skill does decent damage, keep using it.
Your ulti does good damage with kinetic field set up to group things up, it is also great for money on wave 10. Use it to silence casters such as in the tide or techies waves.
Axe is picked for his aoe, his heal and being able to tank things pretty well. His call can also halt the chickens on wave 10 and give you more gold.
Stout - 2 salves - Ring of Protection
Ring of Health - Clarity - 2 more salves
Vanguard - Clarity
Maelstorm -> Mjollnir
Replace Vanguard with Heart of Tarrasque
Black King Bar
Your W makes you lifesteal from your spin and from your maelstorm and mjollnir procs. Healing you for much more than you would expect. You can also use it on allies to heal them if needed. The idea is that this will keep your hp up to tank things and kill them.
Taunt works on everything, make sure to use it on wave 10 to stop the chickens.
You can use your ulti to jump and thus move around on top of the AoE damage and kills it does.
Leshrac is your main AoE damage dealer. The person clearing the most creeps and keeping the lineup afloat when kiting damage is necessary. Early waves just die to the nukes, later waves you still do a lot of damage but need to kite a bit to kill stuff solo if that becomes necessary.
2 Clarities, 2 mango and Healing Salve (salve and mangos are for the stronger wolves in the second half of first wave)
Soul Ring. 2 Clarities, Healing Salve
Arcane Boots, Healing Salve
Octarine, more Healing Salves and clarities if needed
Infused Raindrop prior to wave 8 (mana regen and tank)
Veil of Discord
Sell mana booster from boots and buy Solar Crest, place boots in backpack
Replace Solar Crest (to backpack) with travels for wave 14.
Replace boots with Solar Crest for last wave.
You can not tank waves reliably until you have a heart but can kite them easily with your stun and slow from lightning. The two other spells can then kill the enemy while you keep a small distance to minimize damage.
Your role in the team is to handle one of the spawn sides with minimal help early on and later on apply debuffs and AoE damage when you need to group up.
Techies has the best AoE in the game and is essential in killing the last boss by having a stack of 100+ proximity mines stacked in one spot which you then lure invoker into.
Sobi Mask, Mango, Clarity, Salve
Soul Ring, Boots, Mango, Salve for rest of money
Arcane boots, Mangos, Salve for rest of money
Disassemble Arcane boots to get Octarine Core
Forcestaff instead of boots
Techie should be on the left spawn so he can mine the path from the enemy tower to his tower with proximity mines and later on Remote Mines as well. This will kill most things that spawn there instantly and allow him to hold his lane.
Blast off is a great nuke and should be used to clear out things as needed and help other people as Techie is extremely strong early on.
Medusa is your physical DPS and the main damage dealer to the later stronger bosses but does need some help to get going. The remade Mystic Snake having a stun is part of what makes her great.
Gloves of Haste, Healing Salve
Yasha -> Manta
Healing Salve prior to wave 8
Quarterstaff -> Butterfly
Monkey King Bar
All enemies have mana in this mode. So any time you use Mystic Snake you will get a huge mana infusion, powering your Mana Shield.
Mystic Snake is a stun, so make sure to use it to cancel enemy spells.
Use fortify. All towers on the map are tier 1 towers, so any tower dying refreshes the fortify.
Kiting is very good if you get stuck. Pull them to an ally that is looking strong or just run a lap in the middle. If you pull to base you risk dying and forcing people back to save the ancient. If everybody pulls to base you risk wipes from enemy spells, especially wave 8 with the three Tides that use Ravage is risky that way.
If you need to use a buyback, don't hesitate to use it. Using it too late risks a wipe since other team members might die as well. That being said, don't buyback if your team can handle the wave. The cooldown on buyback and missing item timings can become a problem if used frivolously.
The bottom ward spots are somewhat finicky and the tower vision range isn't correctly shown. So below are ward spots for the disruptor glimpse.