Gaia Support

[Cozmosus]

Gaia support cards will be a series of EARTH Warrior cards usually having "Gaia" in their names, but also include other types for Gaia fusions. Their effects are mostly based upon special summoning or returning from the Graveyard Gaia the Fierce Knight in order to use him for his Gaia fusion summons, which are the base of this decks attack power.

[spoiler=Monsters]Battle Steed of Gaia [EARTH/ Level 3/ Union/ Beast/ ATK 1600/ DEF 1200]
Once per turn, you can equip this card to "Gaia the Lancer" you control, OR unequip it to Special Summon this card in face-up Attack Position. Once per turn, while equipped to a monster by this effect, the equipped monster counts as "Gaia the Fierce Knight". (A monster can only by equipped with 1 Union Monster at a time. If the equipped monster would be destroyed (in battle), destroy this card instead.) 

Gaia the Lancer [EARTH/ Level 4/ Effect/ Warrior/ ATK 1800/ DEF 1000]
During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent. If this card is sent from the field to the Graveyard by a card effect, Special Summon 1 "Gaia the Fierce Knight" from your hand or Deck.

Gaia the False Knight[EARTH/ Level 3/ Tuner/ Warrior/ ATK 1000/ DEF 500]
This card counts as "Gaia the Fierce Knight". When this card is sent to the Graveyard for the Synchro Summon of a Synchro monster, add 1 "Gaia the Fierce Knight" from your Deck to your hand.

Gaia's Messenger[EARTH/ Level 4/ Effect/ Warrior/ ATK 1100/ DEF 2000]
FLIP: Look at your opponent's Set cards. If 1 or more is a Trap Card, add "Gaia the Fierce Knight" from your Deck to your hand.

Gaia the Iron Shield[EARTH/ Level 5/ Effect/ Warrior/ ATK 1800/ DEF 2300]
While this card is face-up on the field, your opponent cannot select other monsters you control a an attack target. You can halve the DEF of this card until the End Phase of your opponent's turn to return 1 "Gaia the Fierce Knight" from the Graveyard to the Deck. Then shuffle the Deck.

Gaia the Twin Swordsman[EARTH/ Level 4/ Effect/ Warrior/ ATK 1900/ DEF 1000]
When this card destroys a monster by battle, you can Special Summon "Gaia the Fierce Knight" from your hand or Deck.

Undead Battle Steed[EARTH/ Level 1/ Effect/ Zombie/ ATK 0/ DEF 0]
If "Battle Steed of Gaia" is in your Graveyard, you can Special Summon this card from your hand. As long as "Battle Steed of Gaia" remains in the Graveyard, this card cannot be destroyed by battle.

Lord Gaia, King of Knights[EARTH/ Level 10/ Effect/ Warrior/ ATK ?/ DEF ?]
This card cannot be Normal Summoned or Set. This card can only be Special Summoned by removing from play 1 "Gaia the Fierce Knight" and 1 Synchro monster you control. This card's ATK become the combined ATK of the 2 monsters used to Special Summon this card. This card cannot be targeted or destroyed by an opponents card effect.

Sea Hexzard[WATER/ Level 4/ Effect/ Sea-Serpent/ ATK 1700/ DEF 1300]
When this card is destroyed by battle and sent to the graveyard, banish the opponents monster that destroyed this card.

Gaia the Sea Master[WATER/ Level 8/ Fusion/ Effect/ Sea-Serpent/ ATK 3000/ DEF 2600]
"Gaia the Fierce Knight" + "Sea Hexzard"
Once per turn, you can send the top card of your Deck to the Graveyard to select 1 monster your opponent controls and banish it. If this card is destroyed by your opponent's card effect, return 1 "Gaia the Fierce Knight" from your Graveyard to your Deck.[/spoiler]

[Time Psyduck]

Rather than 'counts as "Gaia the Fierce Knight", it's '[card in question]'s name is treated as "Gaia the Fierce Knight."'

Battle steed looks OK, although either make the effect continuous or specify a point when it wears off (such as the End Phase). Also, Unions save monsters from effect destruction as well. It isn't something that can be glossed over because you want the equipped monster to go to the graveyard by an effect - but since the union turns it into Gaia the Fierce Knight anyway it's not going to be too much of a problem, and as attacks are basically free opponents would often just attack the Lancer twice.

Lancer is fine - it's a solid beater that summons a somewhat stronger, but just below some key values that make cards good.

False Knight isn't Gaia Support - it's a Tuner that searches itself out at the cost of being unable to run the original, because it being Gaia the Fierce Knight applies in the deck as well (see Harpie Lady). Make it become Gaia the Fierce Knight when it's on the field, and not anywhere else, and it's fine.

Messenger is a good wall, and lets you see what your opponent has so you can deal with it. Searching Gaia is just a bonus.

Iron Shield doesn't seem worth it. It's not easy to summon, things like The Warrior Returning Alive do it's job better, and if it does use it's effect it [i]will[/i] die next turn.

Twin Swordsman seems a bit much - a 1900 beater that gets out a 2300 beater for destroying a monster. Have the summoned Gaia be unable to attack, or attack directly, that turn and it should be fine though.

Undead Battle Steed is a helpful wall/tribute fodder, but nothing special

Lord Gaia is nice, but I would give it an original ATK of 2300 and just have it gain the ATK of the Synchro Monster. That way if it's effect is negated or it's flipped face-down it's not entirely useless.

Sea Hexzard is ok. Nothing special, but that doesn't seem to be the point. More Sea Serpents are always nice though. (The type, however, is "Sea Serpent" rather than "Sea-Serpent". Of the two-word types, only Beast-Warrior is hyphenated)

Sea Master is pushing broken. It's not that hard to summon, and at the cost of a mill (so basically nothing) it gets an improved Chaos Sorcerer effect and can still attack. I would make it a face-up monster, and perhaps send a card from the hand rather than the deck. The return effect is OK, but seems a bit lackluster - if you can tone down the first effect, returning the Gaia to get a draw or something would be OK.

[Cozmosus]

The False Knight is meant to be a help in the summoning of Gaia Knight, and if you put multiples in the deck you could use Undead Battle Steed for a tune up to a non-effect 4 star, which you could then use for Gaia Drake. Undead will also be used for a Zombie Gaia fusion which I am in the process of making. Undead was made to be a wall in order to make it easier for getting Gaia Knight up to Gaia Drake.

The idea of making Battle Steed a union for Lancer is that you could use the equipped lancer for a fusion summon, then get back a Gaia.

I'll fix the errors you've stated and change the OP effects and UP effects. I might get rid of Iron Shield. Either that or change the effect.