Ive thrashed the hard AI's quite a few times with quite a few characters and have since moved on to Nightmare (which, really isnt very difficult either). I used to play a lot of Dota, so the games mechanics came very easily to me. Perhaps I can help a few of you out.
The very first thing Id like to say is, if you have to go back to your base to heal at the crystal, you have done something wrong and are one step closer to losing the game. I have yet to play a charachter who needs to go to the crystal. Nearly every demigod has the ability to heal themselves. On large enough levels, a trip to the crystal means when you get back, your oponent is one level above you. This can happen quite often and you will easilly find yourself 2 or 3 levels below your oponent. That can make things VERY difficult for you. You always want to be at most one level below your oponent. When playing against human oponents, you will inevitably have to go back to the crystal as they will do things the computer wont (chase you deep into your defences, get 3 demigods to focus you, etc) but against the AI, the next time you are back in your base should be when you need to spend money. You can teleport to town, but the best option is play smart and safe untill you go buy your first set of decent items.
Secondly, FLAGS! Probably the most important resource in the game, and the most neglected. Aside from the very nifty bonuses that holding the flags gives you, they also increase your warscore as well as your XP when you capture it. All very important points. The XP for obvious reasons, if you get out there fast enough you can often be level 3 before the first creep wave dies (though on some maps or with slower characters this takes teleport scrolls or the teleport favor item). Even more important then that is Warscore. Not only does it open access in the citadel to VERY important upgrades, it increases your defences (fotresses/archer towers) and these can be essential mid game to keep enemies from pushing too far into your territory (and hence losing more flags that you absolutely must have, like your valor or portl flags). The AI is very diligent about capturing flags on hard and nightmare AI. You need to keep a constant look out for flags you can take. Should you be focused by a demigod and lose a substantial amount of life, enough that you can no longer safely be in the creep wave or "in the thick of it" as they say, instead of running back to the crystal (BAD!) look for flags you can cap. Often you will be able to spend 30 secs, capture a flag (or 2) and gain a level for a skill which can help you out. The important thing to remember here is you are killing 2 birds with 1 stone. You are still gaining experience despite not being in the battle and more importantly you are gaining a flag effect, more warscore and limiting your oponents warscore.
Since we are talking about warscore, I would just like to say a couple of things about the citadel upgrades. I see FAR (nearly everyone) too many poeple being rather selfish and spending all their gold on themselves. This is not the way to win games. Aside from very specific instances it is almost always better to get one of the citadel upgrades (and I mean 1 singular) then spend all your money on yourself. If you have 3k gold, grab an item or 2 for yourself, and get a couple upgrades at the citadel. You will be increasing your entire teams power by doing this as opposed to just yourself. The larger the game, the more effective they are, but even on crucible, they are very important. As to the upgrades themselves, there is much speculation on the added units to waves so I will skip those. I want to talk about 4 upgrades in particular.
First, Offensive and defensive tower upgrades. These are overlooked far too often and can be the difference between winning and losing far too often. For a total of 1500 gold (900 and 600 I believe) you give your towers more health, health regen, more damage and splash damage. The regen and splash damage are whats important of course. Getting these 2 upgrades early on means your towers have nothing to worry about from creep waves. It will require a demigod, and one with a few levels to take down a tower. When playing against the AI, these 2 upgrades alone will keep them from getting very far for a very large portion of the game. I would like to point out that the AI's almost always buy these upgrades ASAP. More importantly, during the early mid game these upgrades allow you to go back to town and not worry that your towers will be pushed down in your abscence.
Next the EXP and Gold upgrades. INCREDIBLY IMPORTANT PEOPLE. The more allies you have, the more important. In a pantheon game (4v4) it is an absolute must. I hope the exp bonus is obvious. 10% exp means you are leveling up 10% faster. If your oponent doesnt have it, great, you will outlevel them if you play it smart. If they do have it, at least you arent being outleveled. The mint is something I think the community as a whole has yet to embrace, but I have found that on anything but very small maps (crucible and prison) it is such an advantage that it becomes rediculous. 4 gold per tick is no joke, the upgrade will pay for itself in just under 7 minutes. For you. During that same time, it will give each of your teammates the same amount of gold. With enough flag captures (and hence warscore) early enough you can get this upgrade very quickly. To make my point, if you were to buy the mint upgrade 2 minutes into the game, and had 3 teammates, at 10 minutes in, your team (this would include you) would be able to buy all Creep wave upgrades up to Giants (as long as you have the corresponding warscore, see flags above ) with the money you have given them. Now, if your playing with AI you cant ask them to spend their gold in certain ways, but the do tend to buy plenty of citdel upgrades on their own.
Lastly, I would like to draw some attention to the most important aspect of this game. DO NOT DIE! Now, of course, you are sitting there saying "But Chaosbrynn, you just told me to never go back to the crystal for healing!" Yes, I did, and one of the major tactics you need to learn in order to master this game is to Not die while not having to go to town. Since we are talking about tournaments here, it is pretty easy. The computer plays conservatively and if you do as well, it is fairly easy to not die. Against players, well, you never know. If your participating in the battles, and manage to lose most of your health it is almost always better to just sit at the back of the battle within experience range, keep an eye out for demigods and soak up experience while you regen. Keep an eye out for easy flag caps while your doing this. If you need to know why dying is bad, well, there is 3 reasons. 1: You are off the field, and hence gaining no money and no experience (income of money stops while you are dead) for the duration of your respawn. 2: You have given your opponents a VERY large chunk of EXP and Gold. Always bad. The best way to be underleveled and underequipped is to give up kills to your oponents. 3: You are now dead, hence not on the field. Your opponents know there is one less demigod on the field and they can now make that push, or hunt down your allies knowiung that they outnumber your team. This rule is SO important it supercedes all other rules. If you are new or havnt mastered certain tactics, and think that regardless of how careful you are that your life is too low and you will be killed, well, go back to the crystal for healing. Its better to do that then die. You do lose out on the exp, but at kleast your income stays and your oponents dont know there is 1 less demigod in the field. I would like to say though that if you do this, make sure to stpop by the citadel. The first few upgrades are VERY cheap and something as simple as giving your towers AOE damage can lead toan enemy demigod being suprised and hence killed. Point being, dont go back just for the crystal, try and make the most of your trip.
Ok folks, that is one hell of a wall of text. Ill stop here for now. Anything else really becomes demigod/team specific so if anyone is having trouble, Lets start a new thread with your character as the focus, PM me to let me know you did such a thing.