jmizzle7, moderator at the ElementsTheGame forum, wrote up an article about how to turn each of the starter decks into something that can reliably beat the snot out of the Level-3 AI.

The thread at elementscommunity

Aether Edit

1. Sell these cards: 1x Abomination, 1x Lycanthrope, 1x Chaos Seed, 1x Nova, 1x Mutation, 4x Spark, 1x Parallel Universe.
2. Buy 4x Immortal, add them to the deck, take out 3x Amethyst Pillars.
3. Fight AI level-0.
4. Buy 1x Dimensional Shield, take out 1x Dagger, buy 3x Aether Pillar and take out 3x Quantum Pillar.
5. Fight AI level-1.
6. Fight AI level-2.
7. you can figure out the rest.

Put your creatures out early and often, use Dim Shield not too early, but when things get hairy.

Air Edit

1. Sell these cards: 3x Thunderstorm, 1x Flying Weapon, 1x Firefly Queen, 3x Firefly, 2x Fate Egg
2. Buy 3x Wyrms, 1x Azure Dragon, and 5x Wind Pillar, add them to your deck, take out any non-Air cards
3. Fight AI level-0.
4. Buy 1x Azure Dragon
5. Fight AI level-1.
6. Fight AI level-2.
7. you can figure it out from there.

It's always better to play another creature if you can afford it instead of spending the quantum on Dive.

Darkness Edit

1. Sell these cards: 3x Parasite, 1x Dusk Mantle, 2x Aether Pillar, 1x Spark, 1x Lightning, 1x Parallel Universe, 1x Immortal
2. Buy 2x Black Dragon, take out the remaining 2x Aether Pillars
3. Fight AI level-1.
4. Buy 1x Black Dragon, take out 1x Quantum Pillar
5. Fight AI level-2.
6. you can figure out the rest.

Use Steal to remove pesky shields or weapons, and save Drain Life for near the end of the match. If you see Emerald Shield, use the Drain Life to take out their most dangerous creatures instead.

Death Edit

1. Sell these cards: 2x Vulture, 2x Boneyard, 1x Plague, 1x Bone Wall, 1x Sapphire Charger, 1x Graviton Mercenary, 1x Momentum, 1x Otyugh, 3x Gravity Pillar, 3x Skeleton, 4x Virus
2. Buy 4x Poison and 6x Mummies, 1x Bone Dragon, 2x Bone Pillars. Take out 3x Quantum Pillars.
3. Fight AI level-0.
4. Buy 1x Bone Dragon, take out 1x Flesh Spider.
5. Fight AI level-1.
6. Fight AI level-2.
7. Buy 1x Bone Dragon, take out 1x Dagger, and there's your deck.

Play creatures early and often, use Poison when you can't put a new creature out.

Earth Edit

1. Sell these cards: 1x Stone Dragon, 1x Titanium Shield, 2x Plate Armor, 1x Enchant Artifact, 2x Earthquake, 1x Cockatrice, 1x Forest Spirit, 1x Heal, 3x Emerald Pillars, 1x Horned Frog
2. Buy 4x Graboid
3. Change your mark to Time.
4. Fight AI level-0.
5. Fight AI level-1.
6. Buy 4x Stone Pillar, take out 3x Quantum Pillar and 1x Emerald Pillar.
7. Fight AI level-2.
8. Keep on trucking.

Play creatures early and often, damn the torpedoes, full steam ahead. Don't bother burrowing your creatures unless you see an Otyugh that gets its health above 3. When playing against an Entropy mark, burrow your creatures when you see them get 8 Entropy quanta, as Antimatter can really ruin your day. Maxwell's Demon can also smack down unburrowed Shriekers.

Entropy Edit

1. Sell these cards: 1x Dissipation Shield, 2x Lycanthrope, 3x Chaos Seed, 3x Mutation, 1x Vulture and the rest of the Death cards.
2. Buy 2x Purple Dragon, 1x Abomination, and 6x Amethyst Pillar.
3. Fight AI level-0.
4. Buy 2x Abomination
5. Fight AI level-1.
6. Fight AI level-2.
7. You can take it from there.

Use Maxwell's Demon against opponent's dragons and Fireflys.

Fire Edit

1. Sell these cards: 2x Fire Spirit, 1x Fire Shield, 2x Deflagration, 1x Rain of Fire, 1x Immolation, 1x Freeze, 1x Blue Crawler
2. Buy 2x Crimson Dragon, 2x Burning Pillar. Take out all the Water cards. Don't sell them, and especially don't sell Purify.
3. Fight AI level-0.
4. Buy 2x Burning Pillar. Take out 2x Quantum Pillar.
5. Fight AI level-1.
6. Fight AI level-2.
7. You can figure out the rest.

Use Immolation on your Ash Eaters to swell your quanta for summoning your dragons, or bigger Fire Bolts. Save the Fire Bolts for later when you have heaps of Fire quanta, then use them on your opponent.

Gravity Edit

jmizzle7 wishes to thank KingofArmagio and Higurashi for help with this deck.

1. Sell these cards: 1x Dagger, 2x Sapphire Charger, 2x Graviton Mercenary, 1x Colossal Dragon, 1x Gravity Shield, 1x Hematite Golem, 1x Graboid, 1x Enchant Artifact, all the Earth cards, and 2x Quantum Pillar.
2. Buy 4x Armagio, 5x Acceleration.
3. That's it, the deck is complete. Go kick some posterior.

Play your Armagio creatures as much as you can, give them Acceleration for a big whammy. Use Otyugh to eat opposing creatures or Gravity Pull so your creatures will beat them to a pulp.

Life Edit

1. Sell these cards: 1x Emerald Dragon, 2x Rustler, 2x Heal, 1x Thorn Carapace, 1x Emerald Shield, 2x Empathic Bond, 1x Fire Bolt, 2x Forest Spirit, 2x Ash Eater, 2x Burning Pillar, 1x Deflagration
2. Buy 5x Adrenaline, 4x Horned Frog, 2x Cockatrice, take out 2x Quantum Pillar, 2x Burning Pillar.
3. Fight AI level-0.
4. Buy 1x Cockatrice, 1x Adrenaline, take out 1x Quantum Pillar, 1x Dagger.
5. You're done, go forth and conquer.

Use Adrenaline on your Horned Frogs, it's better than the Cockatrices. If you see Virus or Parasite, wait to see which creature it chooses to infect before casting Adrenaline, because Poison makes short work of Adrenaline'd creatures. Maby you could add 3 or so mitosis

Light Edit

1. Sell these cards: 3x Pegasus, 2x Holy Light, 1x Solar Shield, 1x Reflective Shield, 1x Wind Pillar, 1x Dragonfly, 1x Wyrm, 1x Thunderstorm, 1x Firefly
2. Buy 2x Golden Dragon and 5x Light Pillar, take out 1x Quantum Pillar and all the Air cards
3. Fight AI level-0.
4. Fight AI level-1.
5. Buy 1x Golden Dragon, take out 1x Guardian Angel
6. Fight AI level-2.
7. you can take it from there.

When fighting Time decks, it's better to use Blessing on your Photons.

Time Edit

jmizzle7 wishes to thank nilsieboy and Higurashi for help with this deck.

1. Sell these cards: 3x Fate Egg, 1x Procrastination, 2x Anubis, 2x Devourer, 1x Parasite, 1x Steal, 3x Deja Vu, 1x Quantum Pillar, 1x Dagger, 4x Obsidian Pillar
2. Buy 6x Ghost of the Past, 4x Precognition, 1x Time Factory
3. That's it, you're good to go.

Play Ghosts of the Past whenever you can. Use Precognition to get more cards into your hand you can use right away, but be careful you don't "deck out" (run out of cards) before your opponent. If you have a choice between playing Golden Hourglass or a creature, play the creature.

Water Edit

1. Sell these cards: 2x Chrysaora, 1x Ice Shield, 1x Purify, 1x Ice Dragon, 2x Photon, 1x Pegasus, 1x Holy Light, 1x Blessing, 2x Quantum Pillar, 3x Freeze, 4x Light Pillar, 1x Quantum Pillar, 1x Dagger
2. Buy 6x Toadfish, 3x Blue Crawler, 2x Fog Shield (they're Air shields, not Water)
3. Change your mark to Air.
4. You're done! and before the first fight even!

Use Ice Bolt and Toadfish's ability Inflate to eliminate opposing creatures. Fog Shield will keep the damage down without eating quantum used for summoning your army of creatures.