Gemcraft

GemCraft is a Tower Defense game released on 2008 and it was praised for its innovation. Its full title is GemCraft Chapter One - The Forgotten. In GemCraft, you are a wizard tasked with defending the world from evil hordes of invading monsters.

Gameplay
GemCraft mixes up the classic TD formula with several new tricks. Your defense consists of magically created gems placed atop towers near the path the monsters follow. Various colors of gem offer different types of special attacks. The primary resource in the game is Mana and you gain Mana from killing monsters. If a monster reaches your Wizard Tower, you lose Mana and if you lose more Mana than you have, then game ends. In other words, Mana also acts as your Lives in the game. You can create gems of any grade directly, though higher grade gems are significantly more mana-intensive. However, the gem you get will be of a random color, so if you want a specific gem type you're better off producing a load of low grade gems and combining the ones you want. Placing a gem in a tower enables it to shoot at monsters. Gems can be dropped on monsters as gem bombs, consuming the gem. You may also place Water Trenches in the path of monsters, slowing them down.

Gem Types
Each gem type has a different ability.
 * Red gems - Splash damage
 * Yellow gems - Chance of doing triple damage
 * Blue gems - Slow
 * Green gems - Poison damage
 * Orange gems - Steal Mana
 * Purple gems - Reduce armor
 * Lime gems - Chance of chain hit
 * Cyan gems - Chance to shock

You can create gems up to grade 6. To get higher grades, you have to combine gems. Gems of different colors can be combined. Dual gems does more damage than Pure gems, but their special abilities are reduced. Combining gems of all 8 colors creates a Prismatic gem.

Levels
There are 48 levels, including the secret levels. There are 5 Epic levels throughout the game which act as Boss levels. Each level has different available gem types. On Epic levels, all gem types are available.

Waves
Monsters come from the monster base in waves. In each wave, monsters have different hit points, armor and speed. The wave stones on the left side of the screen show you the stats of the monsters that will appear. Boss monsters have higher armor and hit points, but there are fewer of them in a wave.

Skills
Completing levels rewards you with XP points which counts towards leveling up your wizard. Repeating a level will not gain cumulative XP as only your highest XP score for each level on each game mode counts towards your wizard level. For each level you get Skill points which you may spend upgrading your wizard's skills.

The skills are:
 * More initial and maximum Mana
 * More Mana gain per kill
 * Armor - Saves mana when monsters reach the tower (Only available when playing from ArmorGames.com)
 * More Mana replenish per second
 * Number of basic starter gems
 * Lower Mana cost for gem creating and combining
 * Powerful gem bombs
 * Dual gem mastery
 * Lower initial and incremental cost for buildings
 * Number of medium grade starter gems
 * Pure gem mastery
 * Number of high grade starter gems

Amulets
Amulets are achievements which give reward you with XP. Battle Amulets can be obtained in each battle, giving additional XP for that specific battle. Journey Amulets are achieved by accumulated stats throughout your journey and each of them can only be obtained once.

Helpful Links
Official Strategy Guide