I've beaten Ridiculous with all the standard factions. It's not that hard if you get an ok start. Tarth was probably the toughest. On Insane you basically have to find an exploit and abuse it. The only game I've won on Insane I used the Titan's Breath -1 turn exploit + Beastlord (i.e. Kulan).To beat Ridiculous you just need to do what you normally do, only better. Not a great deal of room for mistakes, but there are a wide variety of strategies which could be successful.
On Ridiculous, make sure you expand efficiently, make sure your cities are always using their Essence slots. You can always cast Meditation if nothing else. Use the bare minimum of troops which cost maintenance. Rushing the AI is not really an option on Ridiculous or higher, so I personally think you should concentrate on building up as strong an economy as possible. If or when an AI or three declares war on you then fight defensively initially, make use of your faster movement; in your territory you get roads, the AI doesn't, you get strategic spells, the AI doesn't. It shouldn't be too hard to concentrate your forces. Sometimes it's a tough call whether to attack an immobilized stack with your best stack or to put your best stack into a city and use the city defences to help you. Personally in the interests of experimentation I might use a save game to play it both ways and see which works best. The initiative from Freeze and/ or the Dodge elimination from Tremor can be very helpful, but on the other hand so can half a dozen city defenders.
It really helps if you can only fight a war on one front. I don't mind too much fighting three AIs if they all come from the same direction, especially as it's probably only the closest who is regularly sending stacks, but fighting three AIs on three different sides is hard work. Having an AI ally or two can help with this. Make all the treaties you can with the AI you don't want to fight who has the best feelings towards you. If you can eliminate one of your neighbours as a threat and expand in the other direction it really helps. You don't necessarily need to ally with them (although beware of Blood Season when they will go to war with you if not allied), but you just want a bit of breathing space in the middle part of the game.
There are many, many, valid strategies which will work. Decide what your plan is to defeat AI stacks. That normally means working out a way to beat very high armour and dodge. Blizzard works (including Blizzard scrolls). Titan's Breath works. Mass Curse works. Staff troops with blockers works. Heart of Fire + other buffs troops work. Warg mounted troops are great. Ring + amulet troops are great if you have the crystal. Fireball is ok and other spells are ok if you have enough mana and can cast them fast enough (i.e. high initiative). Tremor eliminates Dodge as a problem if you can attack the AI in your territory, very handy against Resoln. Alternatively use a Commander and only train troops in your best fortress (for the level and accuracy bonuses).
Remember to rush building when you can. Play with the tax rate, see if having a higher tax rate actually increases the time it takes to research something. I normally prefer to have a non-zero tax rate, as otherwise all your gold boosts are ignored. I generally go Low or Normal, depending whether Normal has a significant effect on research speed, and whether Normal produces a significant surplus (enough to allow rushing of buildings). If you really want to micromanage, consider designing units which makes best use of your best fortress's production. E.g. if your production is 51, it's better to design a unit which costs 255 to build in that fortress rather than a unit which costs 260, because you will complete in exactly five seasons. Alternatively, you can remember to always rush the last turn of training a unit (assuming you have the gold). Don't let cities sit at +0 growth because they've hit a population cap. Train pioneers or build food increasing buildings.
Speed is everything. Every turn you give the AI to expand is a turn it has to research crazy technology and take city sites and resources which you want. Switch off auto-turn. Make sure your units are always using their maximum movement. Use Tireless March on your best stack. Use minimum movement three units in your best stack (i.e. all troops should be mounted). Make sure Pioneers build cities/ outposts at the end of their turn if they can. Build roads as you are exploring so your Pioneers can get to good city sites you find as quickly as possible.
If you don't like such a speed based strategy, you need to have a plan which lets you beat late game AI armies. Dragons are very effective for this!
If you want to know exactly what strategy I use, I make my sovereign a Mage and my second hero a Commander. They both gain experience in my main stack. The Commander gets roads and then goes down the +accuracy, Command, +initiative, Warcry path. I prefer Death magic because of Mass Curse and Sacrifice, but other magic is viable (especially Water magic for Slow, Mantle of Oceans and Blizzard, and Air magic for Haste, Guardian Wind, Titan's Breath). If you're using Life magic then cast Sovereign's Call early on your cities, it's a great spell. Heal + Wraith and Lightbringer can win you early battles. If you're using Death magic then Raise Skeleton is free, Raise Skeleton Horde is quite expensive but potentially wins battles. Summon Air Elemental is a powerful spell if quite expensive. Cast tactically it knocks down all prone vulnerable units in one tile, no chance to resist, which is very handy.
Don't use more mana than you have to, but don't be afraid to cast spells if it means your units take less damage. The more you can keep your units alive the more you can clear lairs and quests, and if you can get two heroes in your main stack to level ten or so then I think you're well on the way to winning. Once you have Deadly/ Epic Stack of Doom the game is a lot easier.
As I say, do what you normally do, but better. Have fun.
