Gnoll
GnollHealth: 6Attack: 3Shots: noneMovement: ground
50 gold (12)Hex size: 1Defence: 5Dmg: 2-3Spd: 4 (extra slow)
Above-average level 1 creature with good defence ratings and damage.
 
Gnoll Maraudeur
Gnoll MaradeurHealth: 6Attack: 4Shots: noneMovement: ground
70 gold (12)Hex size: 1Defence: 6Dmg: 2-3Spd: 5 (slow)
1 speed, 1 attack and 1 defence for 20 gold extra? Bad upgrade looking at the value, also costs 10 wood to upgrade the dwelling, so it's not worth doing unless you're really wealthy.
 
Lizardman
LizardmanHealth: 14Attack: 5Shots: 12Movement: ground
110 gold (9)Hex size: 1Defence: 6Dmg: 2-3Spd: 4 (extra slow)
This table shows lizardman stats with the latest game patch applied. Originally they've had 12 hit points, 1-3 damage and population of 8. A much-needed balancing for Fortress.
 
Lizard Warrior
Lizard WarriorHealth: 15Attack: 6Shots: 24Movement: ground
140 gold (9)Hex size: 1Defence: 8Dmg: 2-5Spd: 5 (slow)
With the latest game patch, lizard warrior cost went up from 130 to 140, attack from 5 to 6, defence from 7 to 8, health from 12 to 15 and damage from 2-3 to 2-5! So what you are getting now is quite a decent shooter with excellent health and defence. This creature upgrade is excellent value for money, so you must do it. I'm glad the balancing took place, even though fortress is still unfairly weak in the mage guild department, this goes some of the way to make it average. Bless/curse will make a lot of difference to lizard warriors.
 
Serpent Fly
Serpent FlyHealth: 20Attack: 7Shots: noneMovement: flying
220 gold (8)Hex size: 1Defence: 9Dmg: 2-5Spd: 9 (ultra swift)
Special: dispels all beneficial spells on the target.
Costly and weakish. Damage range is big, strongly affected by bless or curse. Attack enemies that have many beneficial spells on them, enemy will be really frustrated if he spent few rounds casting bless, haste, shiled or something like that on one creature and it all goes off in an instant. Useful for blocking enemy shooters, especially with their reasonable defence ratings and speed. Also good to give to scouts for lots of movement. Before the patch their attack and defence was lower by 1 point each.
 
Dragon Fly
Dragon FlyHealth: 20Attack: 8Shots: noneMovement: flying
240 gold (8)Hex size: 1Defence: 10Dmg: 2-5Spd: 13 (very quick)
Special: dispels all beneficial spells on the target. Attack casts weakness on enemies.
Before the patch dragon flies had no weakness special and att/def of 6/8, so the upgrade became much more reasonable. Dragon fly's speed can only be beaten by efreet sultan (he has the same speed) and some of level 7 upgrades! That means you will often be the first to cast the spell in combat (haste would be nice to keep it that way). Now the fly use is really strategic - remove beneficial spells and add weakness! Flies are very annoying to spellcasters. If you have spare slots in your army, split the flies so that you can dispel and weaken more enemies.
 
Basilisk
BasiliskHealth: 35Attack: 11Shots: noneMovement: ground
325 gold (4)Hex size: 2Defence: 11Dmg: 6-10Spd: 5 (slow)
Special: 20% to turn target to stone, stone lasts for 3 turns, stoned enemies take 50% damage, unstoned if attacked.
Finally a better creature, normal for level 4. Useful for both offence and defence. Stoning abbility can be especially nice to block the holes in your seige walls for a while with... stoned enemies!
 
Greater Basilisk
Greater BasiliskHealth: 40Attack: 12Shots: noneMovement: ground
400 gold (4)Hex size: 2Defence: 12Dmg: 6-10Spd: 7 (extra swift)
Special: 20% to turn target to stone, stone lasts for 3 turns, stoned enemies take 50% damage, unstoned if attacked.
Good upgrade, improves basilisks all-around.
 
Gorgon
GorgonHealth: 70Attack: 10Shots: noneMovement: ground
525 gold (3)Hex size: 2Defence: 14Dmg: 12-16Spd: 5 (slow)
To compensate for the previous creatures, fortress rules in level 5. Gorgons are very tough, but try to save them until the upgrade, that's where they become extremely valuable.
 
Mighty Gorgon
Mighty GorgonHealth: 70Attack: 11Shots: noneMovement: ground
600 gold (3)Hex size: 2Defence: 16Dmg: 12-16Spd: 6 (swift)
Special: 10% chance of killing 1 top creature of enemy stack per 10 mighty gorgons attacking.
One of the best upgrades in the game, we can forget the minor stats upgrades, the special abbility is awesome! Yes, even if it's an archangel commanded by a hero with 30 defence, he can die instantly from mighty gorgon's gaze. The more mighty gordons you have, the more enemy creatures will die straight away from the death stare. Group of 50 mighty gorgons will usually kill between 2-7 creatures outright just with their stare. Attack high level enemies, so that the special will be more effective. Take note that it only works on living creatures, sadly. If you have less than 10 mighty gorgons, splitting them into little stacks can increase the chance of their gaze working.
 
Wyvern
WyvernHealth: 70Attack: 14Shots: noneMovement: flying
800 gold (2)Hex size: 2Defence: 14Dmg: 14-18Spd: 7 (extra swift)
Below-average level 6 creature. Damage is ok, but wyverns die quickly because they are the only strong flies in fortress...
 
Wyvern Monarch
Wyvern MonarchHealth: 70Attack: 14Shots: noneMovement: flying
1100 gold (2)Hex size: 2Defence: 14Dmg: 18-22Spd: 11 (quick)
Special: chance to poison living enemies (stack's maximum health will be reduced every turn, can be removed by cure spell).
Costly upgrade raises the damage by 4 and adds a poison abbility which can be very useful to weaken a strong stack. Hit points are very low for level 6 upgrade, so use wyvern monarchs as an offensive unit to finish off the weaklings and to try to poison really strong stacks (better do that after they used their retaliation). Remember that only living creatures can be poisoned, therefore an undead army should be considered a serious threat (as well as conflux elemental army in AB expansion).
 
Hydra
HydraHealth: 175Attack: 16Shots: noneMovement: ground
2200 gold (1)Hex size: 2Defence: 18Dmg: 25-45Spd: 5 (slow)
Special: attacks all adjacent hexes, no enemy retaliation.
Costs no special resources and the special abbility is one of the greatest: hydras attack all 8 hexes around them without fear of retaliation! Speed is appaling for a level 7 creature, but if you use hydras strategically, they can cause more damage than even angels: always position hydras to touch as much enemies as possible at once. When hydras retaliate, they do the same 8-hex attack, this way enemy troop can cause damage to a whole group of his by attacking hydras. Use spells like bless, haste, teleport and counterstrike.
 
Chaos Hydra
Chaos HydraHealth: 250Attack: 18Shots: noneMovement: ground
3500g+1s (1)Hex size: 2Defence: 20Dmg: 25-45Spd: 7 (extra swift)
Special: attacks all adjacent hexes, no enemy retaliation.
Extra 75 hit points, 2 attack and defence, but most importantly extra speed. Well, speed still remains the slowest among level 7 upgrades, but the strategic use is at it's best. If you manage to get close to enemy shooters, enemy will have no painless way of getting rid of your hydras: if he attacks them with all he's got, all he's got will get the damage and if he tries to wait, hassle his shooters to death. Still, without the expert teleport/haste spell, chaos hydras are not very dangerous when stand against the castle walls.