Advice for Verdant Mages
Verdant (Green) mages, a word of warning: Phoenixes although seemingly a capable unit are fraud with weaknesses so be careful in using them. When using phoenixes you will have a very low ressurection ratio and most capable attacking mages will find it easy to penetrate your defenses if you have them in first stack. Instead, use a horde of treants in conjunction with the spell Plant Growth. The higher the spell level the better the plant growth will function so always keep an eye on the black market for spells that you do not yet posses to increase your spell level. Being favored by the god 'magic' will also further increase your spell level whilst not increasing the cost or Power rank of your Treants.
An advisable defensive assignment is Rust Armor in conjunction with either Scroll of protection from Fire or Ash of Invisibility. The Former will serve to guard your weakness against fire whilst the latter would take care of aggressors using the Spider's Web which can seriously affect your unit's initiative.
Another interesting twist verdant mages can use is to augment your forces with some ascendant units, such as archangels. Be careful, however - your first objective should be to maintain several tens of thousand of treants (as many as you can). A further augmentation to your stacking could be Dryads and Nymphs which are very powerfull units in stack 5+, where they'll not be attacked. Even non-Verdants should have 10,000 Dryads and 2,500 Nymph, so Verdant should definately too.
Note that like ascendant creatures, many verdant creatures have natural healing or regeneration abilities. While they don't work quite as effectively as ascendant creature abilities of this type, they do still work well. Enchantments on your Kingdom MUST include Plantgrowth if you are intend on using treants, additionally Sunray can be very useful aswell.
As hero a high level Shaman is recommended which will further increase the strength of your Treants.
Green:
Greens are nice to play if you want to play fast and gain much lands as possible. Problem arises from reds and deviled blacks. When playing green, it is important to have a tough stacking that is capable of taking damage. I recommend avoiding contact with black mages since they always have access to devils. Reds can be handled though with efficient stacking. Most of the time, you will not have problems winning combats with a good stacking.
When researching, keep in mind of the limited resources you got and use the werebear/gorilla stacking enhanced by enlarged animal in both offense and defense. As your spell level goes up so does your animals. Watch out for ring of animal command. Don't piss off too many mages. Concentrate on research first. Don't worry, you'll be up in rankings in almost no time.
When playing green, you need to rely on your defense capabilities. The key here are treants. Rule of thumb is that if you have enough, you can defend your country most of the time. Nymphs and dryads help in offense but suck in defense so disband them or keep them in low numbers when defending. Phoenices are optional in defense and recommended in offense so that you can always deal more damage than your treants are capable of. Use web of spider woman when defending in low ranks and rust armor when defending in higher ranks. Rust armor is good for offense against reds, greens, and blues, sword of light against blacks, and call hurricane against whites.
When playing in higher ranks, control the numbers of nymphs and dryads. You can use blood ritual (if you have the spell) and add pegasus as fodder troops. It is important that you have at least a casting of phoenices guarding your country. The bulk of your army will remain with the treants. No attacking blacks please. If you have to, shift to a treants/gated troops and equalize the stacking power. High barriers are always important for defense since most of the time, reds will be attacking you. Inferno and flameshield will obviously ruin your country (once they get through so be in guard). To be able to counter to reds, you must use at least two castings of phoenices and treants backing you up with some fodder ranged troops. Rust armor + head of medusa will definitely rock the offending red if both of them went through. Another possible combination is rust armor + carpet of flying. Expect his troops to be roasted once it went through.