I want to cultivate Discussion on what the best pure nature cards are for each orb, and what spells are most cost effective.
I will list below what units i find most effective and universal for most PVE and PRVE maps.
1 orb units
Swiftclaw-high damage, can rush structures easily, and very good at killing units fast (medium units are generally easier to manage and don't get locked down from Small knockback)
Shaman-your main ranged damage unit and healer, can attack air (I started replacing other ranged teir 1 units with shamans. Their heal+damage is still useful even in t4 as XL support units.)
TreeSpirit(both)-Extremely good at defending and attacking, can take on most 2 orb cost units without problems.(These were added pretty late in the game's life. They have so many insane pro's you can actually use them as your only t1 unit if you have enough charges.)
Dryad(both)-great unit for general buffs with both versions, a must have on maps that have specific enemies that are really hard to deal with early (her paralysis can lock a unit down indefinitely, provided you don't accidentally shoot the stunned unit,)
Amazon(green)+Werebeasts- This combo makes Werebeasts regenerate 50% more, making them an amazing tank unit for long sieges and distracting enemy mobs (this unit combo is nice if you are trying to assist a teammate without needing to babysit your units.)
WindWeavers- useful ranged units, can shoot two different units at the same time. (these used to be the mainstay of t1 nature, but since treespirits and swiftclaws can bust through bases and objectives faster, they are now more effective as wall defenders)
2 orb units pure
Spikeroot-Great card to get along with having TreeSpirits (only shoots ground, but does tons of damage and has pretty high building damage)
Parasite Swarm-At max upgrade state you can take medium cost t3 units (Since nature is about control, t2 is more about taking their best units and stunning the rest while you kill their buildings or required objectives)
Burrower- great unit for killing buildings/objectives (if you spawn two and get them to spit on the same wall segment, it instantly destroys them)
Deep one(both)- Amazing unit with very strong damage and health (both affinity catch's are great for pulling in units you need to kill first, or pulling units you want to capture without risking parasite swarm squads)
Mindweavers(both)- very strong against air units (is a good counter to units with strong ice shields since their poison does direct health damage)
3 orb units pure
Razorleaf- great siege and defend unit (for most cost effective strategy have two Tree Spirits linked with it for maximum damage)
Fathom Lord- Great unit for killing bosses and extra large units (at max rank only costs 25 to paralyze)
ThornBark- great linked fire unit for killing mid-late game mobs (can be used as offense, but their lack of range makes razorleafs better in offensive roles.)
Deepcoil Worm- great siege unit, with awesome tunneling mechanic for moving lots of units around the map fast (generally great damage at t3, and the tunneling ability makes them invaluable for larger maps with struggling teammates)
Swamp Drake- Great for maps that need hard to reach objectives killed (also good defense units vs other air units and ground mobs that can't retaliate)
Timeshifter Spirit- Insane unit that cancels all ranged attacks and stops all enemy abilities from being use-able (doesn't stop monsters from spawning at buildings, so that's a bit disappointing)
4 orb units
Colossus- Great unit for endgame bosses and units (has a nice roar that silences enemies)
Grimvine- Good unit comes with nice root CC (more useful in splash decks as only needs 1 nature orb)
Giant Wyrm- Strong air dragon that has high damage and does more damage the longer it attacks
Primeval Watcher- good unit for defending against mobs (this unit is great if you want a low unit base defense solution vs trash mobs later in the game, otherwise there are stronger offensive options)
Forest eldar-Great offensive unit that can heal friendly units (this unit makes other tier units scale better with a constant group heal)
Grove Spirit- Great unit for healing units in entrenched positions (she has a channeled AOE heal, making her extremely cost effective)
Spore Launcher- Great building killing Siege unit with linked fire.
Breeding Grounds- A must have building that makes all your units cost less!
shrine of memory- good card that is more viable with a spell heavy deck (if you use spells they go directly into void power, when using units their void power doesn't come back until they die)
Fountain of rebirth- a good building for larger pve maps where your t1 and t2 fights are difficult (heals all friendly units in the game, so using it in co-op missions is a very good idea)
Healing gardens- Great building if you are using regenerating units, and is a good combo with ranged units for base defense.
Lifestream- insane damage reduction building. Reduces damage done to 20% in a given area, 40% of that damage is directed at this building (that means 60% of total damage received is completely negated)
Living tower- great building with the linked fire mechanic (if you didn't bring windweavers you can set these guys up behind walls and they do pretty good damage.)
Mark of the keeper- Great base defense tower that cancels all ranged attacks and abilities from being triggered
Primal defender- good air defense building vs large amounts of units (can attack ground but is better to use units as they can attack after)
Tunnel- a nice building for defense maps where you need to have mobile armies to defend multiple objectives (it's a nice card but deepcoil Worms are generally more versatile)
Wheel of Gifts- Great building with extremely good buffs (you will want to make 3 in a game, as they each can activate 1 permanent buff)
Surge of light- Amazing AOE heal. This is the staple of nature spells, you will always want to bring this card, as it's one of the best scaling cards in the game.
Creeping paralysis- great Crowd control card that has a longer CC than any other nature card.
Curse of Oink- Great crowd control card, but you don't want to attack the units affected as they will become unoinked sooner.
Ensnaring roots- great card that makes ground units unable to move (more effective against melee units)
Enlightenment- Game changing card that makes you able to use ANY card in the game without the orb requirements
Hurricane- useful card for killing and disabling large mobs of small units (some maps have insane amounts of archers that attack you at t1, otherwise not a very useful card later in the game)
Mind control- Makes you able to permanently use an enemy unit (excluding unique map bosses and such)
Parasite- Good against large mobs of weak units and air units (the parasite jumps to a new unit if it kills the targeted one)
Noxious clould- Great card against large stationary mobs.
Revenge- a good damage reduction card (makes enemies take 20% of their own damage, reducing your units taken damage to 80%)
Regrowth- Insane healing card for t4 nature (best healing card in the game)
Ray of Light- Good healing card that heals a Percentage of total health (heals 3% hp per second, so is better for high health units)
If i left any cards out, I don't think they are very useful :P.