Wow, that's a lot of stuff. I definitely agree with most of it, and it all sounds very cool. Just my few nitpicks:
More quick notes on elemental powers, masks, and tools (this time, I'm assuming seperate attack button):
-Fire: Holding down attack button can charge a fireball (think like a bow's flaming arrow). Attacking enemies has a random chance of setting them on fire, and fireballs act like Flint and Steel on contact with a block or enemies. By attacking existing fire or lava, heat can be absorbed, turning lava into temporary cobblestone and putting out fire. When near lava or fire, Elemental Energy will regenerate at a slightly faster rate than normal. Guarding with a fire-based weapon will automatically absorb all nearby flame, including flame on the player.
-Water: Automatically get more maneuverability in water, as well as a longer air meter. While on land, holding the attack key will create a jet of water, which pushes foes back and does minor damage. Underwater, this becomes a powerful riptide (essentially a temporary current). Mining underwater is not slower than mining on land, unlike the usual mechanics. By holding the attack key and pointing at water, it can be absorbed for Elemental Energy (though this is slow compared to other elements). Charging a water jet for long enough will cause it to create a temporary water block upon impact. EE regenerates more quickly while in contact with water, or when near (~10 blocks in any direction) water.
-Air: -25% gravity, takes reduced falling damage. By jumping in midair, the user will be boosted a short distance upwards and in the direction pointed. Holding the attack key creates a gust of wind, which costs almost no elemental energy and pushes enemies quickly away. Using this underwater results in a partial refill to the air meter. The player's speed in climbing ladders and vines is increased as well.
-Earth: By attacking the ground, a pillar of earth can be caused to erupt from the ground (does not work on sandstone, cobblestone, or other artificial materials). This flings foes into the air, leaving them to die by falling damage. By holding down the attack key while pointing at the ground, an earthquake can be caused, stunning nearby enemies and dealing radial damage. By hitting the "place" button with elemental powers/Claws selected, a block of dirt can be created. Mining with bare hands or Earth Claws will regenerate Elemental Energy.
-Ice: Attacking foes has a high chance of freezing, can charge up an ice blast that creates an ice block wherever it hits, can attack snow or ice to regain Elemental Energy, Elemental Energy regenerates more quickly in cold areas. Frozen mobs act as solid blocks until they thaw (which, if codeable, takes longer in cold areas). Traction is drastically increased when on ice.
-Stone: Physical attacks deal more damage. Attacking the ground on sand, stone, clay, sandstone, or cobblestone will cause a small boulder of that substance to be created (I'm picturing this as an entity with the textures of the surrounding block, about the same size relative to the player as Kohlii balls are to the Toa). Attacking this boulder will allow the player to kick/punch it around. The boulder will deal damage to enemies it rolls or flies into, and will also deal varying damage depending on the substance (if doable; Stone and Cobblestone might do more damage than sandstone). The boulder can be removed by mining it, and kicking it with Pohatu's Foot Additions will cause the boulder to go farther, faster, and deal more damage.
Then for the Kanohi, I at first thought that you would want a seperate button to trigger them. However, I soon realized that almost all of the early Kanohi (except for Noble Kanohi) were essentially ambient effects, so that wouldn't be needed. As such:
-Hau: Will protect against attacks from anywhere in the player's range of vision. However, the shield has a limited amount of durability, and will break after taking enough hits. It will slowly recharge if not hit for long enough. The player can guard with any weapon to quickly recharge the shield.
-Kaukau: Allows the user unlimited time underwater.
-Miru: If the user holds the jump button in midair, then they will glide slowly downwards. If combined with the Elemental Power of Air, then the user can glide upwards as well (though this is not as fast or hard to control as Creative Mode's flight, and it is still slightly difficult to rise upwards).
-Pakari: Physical attacks deal double damage, blocks are mined twice as fast.
-Kakama: Holding the Sprint key will result in a sprint that is twice the speed of the usual sprint.
Powerless Kanohi can be forged by using a Crafting Table, and then put in a furnace to become regular Kanohi (whether it's Great or Noble will depend on the type of Kanohi).
Most Noble Kanohi would probably need a seperate button to trigger them:
-Huna: When triggered, the user becomes invisible. Mobs cannot detect the player unless they are in motion, and there's a random chance that mobs will not detect a moving player either. Players cannot be detected at all in mid-air. Pressing the button again when invisible, being hit while invisible, or spending too much time invisible, will cause the player to revert to normal.
-Rau: This is more of a "story mask" in my mind. To players using this mask, Matoran carvings and such found around the island are translated automatically. These could be trivia or story info. In addition, this mask makes it easier to tame mobs such as wolves (which I'm guessing would be replaced by non-infected Muaka or something?).
-Mahiki: Pressing the button causes the user to create an illusion. The illusion travels forward in a straight line, jumping over gaps and blocks whenever possible. The illusion vanishes if it hits a wall it cannot jump over, or if it takes any damage (this includes falling damage). Mobs will automatically attack the illusion instead of the player, assuming that both are in their detection range. The inspiration from this actually came from a hologram power in Halo: Reach.
-Ruru: The player can see clearly any objects or mobs, regardless of the lighting.
-Komau: The player can take control of nearby mobs by pointing at them and pressing the Kanohi button. The player will then get a third-person view of the mob, and can control them for a limited amount of time. Mobs will not attack other mobs.
As you can tell, some (such as Mahiki and Komau) are more useful in cover.
Now, here's my take on the Toa Tools:
-Fire Sword: Attacking enemies has a small chance of igniting them (this chance is increased with the Elemental Power of Fire). Guarding with this (when using the Elemental Power of Fire) will absorb all nearby flame for Elemental Energy.
-Hooks: Mining and attack speed are not affected by being in water, allows user to deal more damage underwater.
-Axe: Deals more damage in the air or in a jungle biome, is more effective at cutting down trees.
-Earth Claws: Shorter range, deal more damage, can mine more quickly than most tools (do not get blocks from mining "better" materials, such as stone).
-Ice Sword/Ice Shield: Guarding animation is changed to a defensive block with the Ice Shield, attacks have a chance of freezing enemies (chance increases when combined with Elemental Power of Ice).
-Foot Additions: Deal more damage, attacking animation changed to a kick, attacks are slightly slower. Attacks deal more knockback to mobs than usual. Attacks will also kick a boulder created with the Elemental Power of Stone farther and faster.
I'm picturing them as difficult to get, but unbreakable.
As for the Turaga's tools:
-Firestaff: Attacks have about a 25% chance of igniting enemies, deals less damage than Fire Sword.
-Trident: Attacks are more effective underwater, deals more damage.
-Kau Kau Staff: Holding the attack button (weapon, not elemental) will cause the buzzsaw at the end to activate, which causes repeated damage but no knockback to hit enemies.
-Drill of Onua: Highly effective at mining, can mine any materials.
-Ice Pick: Increased traction on ice (stacks with the Elemental Power of Ice's buff as well).
-Stone Hammer: Shorter range, deals increased damage and knockback to enemies. A slightly slower weapon.
For the Turaga's tools, I'm imagining them as easier to get, but still unbreakable.
Golden Kanohi just stack all of the other mask powers.
I have some ideas for 2002-based events and gear, as well as some 2003, but I'll save those for later.