Tricks

Harpy Hag Hoodoo

Since they are fast, and strike with no retaliation, Harpy Hags can be used to attack neutral stacks which are much more powerful than they are. To make this work, you need to be facing enemy troops with a speed of 4 or less, or use the Slow or Haste spells so that your Harpy Hags are moving more than twice as fast as the enemy (or some fortuitously-placed obstacles). You then can use the Wait function to make the enemy move first, swoop in and attack, then, when they get close, hustle to a new location and repeat (beware Morale bonuses by the enemy however!). In a multiplayer game this can take some time to do and hence is frowned upon, but early on in a SP game you can use it to clear mines/guardians you would otherwise not be able to, at least until your Dragons become available. This tactic can basically be done with any non-retaliatory creature (Cerberi, Arch Devils, Sprites, Vampire Lords), but the HH's are the only one to return to their original hex.

Cooking the Books with the Dwarven Treasury

The Dwarven Treasury can be extremely useful during long games on larger maps. If you let your gold accumulate week to week, buying only essential troops and buildings, in a month or so your gold stockpile can mushroom to humonguous levels (1 million gold or more). The interest rate is equal to Treasuries Owned x 10%, so if you have 4 Rampart towns with Treasuries, that's 40% per week. If you start with say 100,000 gold, with a daily income of 10,000, you will, after 4 weeks, indeed have over 1 million gold. But the downside is that a Plague will kill off half of all unbought troops in your towns, so I'd start saving AFTER a Plague (as I've never seen two Plagues happen within 2-4 months of each other).

Wraith Bomb

Wraiths can be useful after all! Send out waves of expendable heroes against a dangerous invader, each with 7 1-Wraith stacks, with the aim of reducing his spell points. You will need lots of extra gold of course to make this work. This of course works better against the AI than it does vs. another human, and is countered by Destroy Undead, but if you have the Pendant of Death...! And even getting your enemy to cast Destroy Undead over and over is going to cause him to lose spell points. Considered a "gamey" strategy by some...

Castle Siege

Attacker Hypnotize an enemy troop and open the drawbridge.

Six or seven stacks of cyclops kings can reduce a castle to rubble in as little as two rounds.

Defender Block an open drawbridge with Force Field.

In a Tower town, send a lone gargoyle to stand on the top or bottom mine after at least one ground troop has advanced all the way to the castle wall, leaving several hexes between the gargoyle and the nearest ground troop. In many cases, the ground troop will walk through every mine on the way to kill the lone gargoyle, and sometimes die before it reaches its target.

Open-field battle

Remove Obstacle is a possibility when:

• a troop in your army is blocked in its starting position by a battlefield obstacle.
• an enemy shooter is protected by a battlefield obstacle.

Extra nasty Berserk

If you have Berserk, and are fighting at least two stacks of Dendroid Guards and/or Dendroid Soldiers, try using it to get them to attack each other. If you do, they will bind each other, making them both unable to move.

Using Master Genies

When you have Master Genies on your hero and have several creatures slots free, split your Master Genies to several stacks so you could benefit from their spell casting ability with additional casts.

No spells, or?

The Orb of Inhibition seems slightly bugged. It doesn't stop the Armor of the Damned or the Angelic Alliance from casting their spells at the start of combat. Especially in the first case, this can give you an enourmous advantage.

It goes on and on

Clone helps double your manpower if you cast it on troops that number well over 500 (5 or 10 if it's concerning LV4+ troops). They also still retain their abilities, so that means you can spam Resurrection with Archangels, general blessings from Master Genies or even deliver the extra deathblow with Dread Knights, Cyclops Kings and Power Liches.