Rents!! Obviously. I'll disclose each Archetype deck and why.
Yeah, just hit this rank, but to be fair, I could only get to Gold 2 before getting a Ruler of The Seas delegation (that was a high rank already), it helped a lot since we face too many over power decks, Yodins, Mylors, cards lvl 2,3,4,5...
Ok, first, good cards won't make any difference if you don't know whats the best Strategy for Each Rule, what set of cards can evade and hit more, which abilities counters what, the notion of what your opponent might use or what can be obvious that you will use... I'll give some Tips that I learned about rules.
FIRE ARCHETYPE
Kobold - Is usefull on low mana battles since he fits in many formations.
Cerberus - So good for too many rules, like the Opportunity, Melee Meyhem (attacking from anywhere) and Super Sneak. If any of thoses rules above goes together with Earthquake, Poison or Unprotected, he is also really good because of the Heal. He can also survive well on only poison or earthquake anyway.
Talia - Good for Silenced Summoners rule. Makes you win some battles because of extra mana (for real).
Forgotten One - Really good on high mana Poison battles since he doesn't get nerfed with Immunity ability, even surviving at the end, he can finish it with high attack, hp and shield.
Tusk The Wide - A good Tanker if you think your opponent goes with magic dmg.
Scorch Fiend - The zero cost permits him to be in all low mana battles, he can take first hit from Opportunity or Stealth monsters and protect others low hp team mates.
Grum Flamable - I'm still getting used to this orc, but he is very good if gets at least 1 kill, sometimes he will take carry of the match alone.
Cards playable for all:
Serpentine Spy (for so many reasons) ; Antoid Platoon (good mini tanker in some positions and rule sets) ; Living Lava (thats the tanker) ; Scavo Chemist (Helps with the Cleanse ability on Poison rule).
I'll tell already the others normal cards that fits well with fire decks, which are:
Elven Cutthroat, Battering Ram, Uraeus. All thoses because low mana battles can be an advantage to use many melee monsters as possible. Sometimes also using Creeping Ooze, since speed can be a determinant for many reasons on thoses ocasions. Depending if is a high mana battle, Sand Worm can be a good choice. Desintegrator card is really good with Demoralize on thoses same ocasions that I talk about Cerberus.
WATER ARCHETYPE
Alric - I'll start with him since I think that card is half of the reason I climbed so high, he can combo well with so many others rented magic cards...
Venari Wavesmith - He is not in this image because I already own it, and it is still meta, helps with the Protect for the team.
Captain Ghost - This guy is so good on high mana battles, the Affliction ability debuffs the Heal or Tank Heal on first opponent monster (that normaly is a tanker), while also doing good dmg.
Kelp Initiate - A good mini tanker in many ocasions, also in second position on Explosive Weaponry rule set (the Blast one) absorving the adjacent dmg. He is also fast to evade.
Lobstradamus - Good tanker that mitigates melee dmg (if you think you adversary goes with it), hitting 2 dmg with Alric while that, can also be used in last position on Super Sneak rule.
Nerissa Tridawn - She is sooo good, high dmg, high hp... Also high mana.
Wave Brood - I don't use much, but the Taunt ability with high hp can be usefull to ensure the others to survive e do dmg.
Oshannus - Previous meta mvp card.
River Hellondale - This is an interesting card I've been testing with the Resurrect ability.
Torrent Fiend - Same reason for all thoses zero mana legendaries, fit in every low mana battle.
Sea Genie - I don't use much, but he goes well depending on the combo of rule sets and mana, mainly for Earthquake having the Flying ability, hitting 3 magic dmg (with Alric) is a good option keeping him in a protected position due to low hp. (5th slot for ex).
Baakjira - Nice magic tanker, thats it.
From the playable for all cards:
I use Ice Pixie a lot. I like the River Nymph, since the Cleanse makes it better than Medusa or Elven Mystic (that are also 4 mana cost). Very few times I use the Serpent of Elf and the Demonshark.
About normals: The Enchanted Pixie is a good rent for water deck, also due to the Flying ability and to fit on some mana battles. The Magi Of Chaos is also really good and its not there because I found it already. I use both with some moderated frequency. The Creeping Ooze is usable in any deck.
EARTH ARCHETYPE
Goblin Sorcerer - I use him sometimes if for some reason I expect low hp monsters in the adversary back line.
Wood Nymph - I really like to make a double heal deck with her and Goblin Psychic, however she has low hp and can die fast. If it is a battle Earth X Earth, I like to use Unicorn Mustang upfront tanking magic dmg and getting healed, this formation is very good in Bronze and Silver league, also with the help of the following card:
Mushroon Seer - This formation above together with this card is really good. The Silence ability that gives -1 magic dmg is letal against Alric, Obsidian and Delwin Dragonscale.
Xander - Rarely used with low mana, few options of archtypes, and the Silenced Summoner rule.
Grund - I tryied to test it sometimes, I just don't know exactly in which ocasions he does better...
Fungus Fiend - Zero mana auto explainable.
Djinn Biljka - I found this one already and sometimes I use it together since Camouflage is an extra protection.
From playable for all:
Besides thoses that I talked before, the Regal Perylton is really good and can Evade a lot with High Speed and Flying. Mycelic Slipspawn also seens a good card, however I don't use with much frequency. And the Khmer Pricess low mana cost can help to fit on formations. I used Failed Summoner a lot last meta, but not at all on this one. Mycelic Infantry is also a good card, good tanker against melee.
From normals:
Enchanted Pixie and Magi of Chaos can also do well here depending on conditions. Also Creeping Ooze.
LIGHT ARCHETYPE
Chanseus The Great - I rented to test and he is really good with Resurrect, Repair and Triage, so you don't need to use Armorsmith, also heals some back line monster that took most dmg. He has high mana cost of 7, and the rent was for 4.5 dec per day, I think it was the most expansive card.
Lorna Shine - Divine Shield can be really good in low mana battles.
Djinn Renova - I always keep using her, already has an ok hp, gives extra hp for all with Strengthen, does dmg... I like this card
Soul Fiend - Same stuff...
Prismologist - I got one and is really good with the Blast.
Cards playable for all:
I'm still trying to get used to this light deck. I mainly use Chaos Knight or Shieldbearer as tankers, Luminous Eager as secondary attacker, Celestial Harpy with low mana and Opportunity, Time Mage with Slow, Truthspeaker with Protect, Pelacor Albarest with Double Striker, and Venari Crytalsmith with Heal. I'm not really good with this deck and don't have an especific formation, I try to choose between thoses, and the others I don't use.
DEATH ARCHETYPE
Zintar Mortalis - One of the previous low mana meta summoners, out o rotation, but I still try to use some tactics from previous seasons together with Haunted Spirit. I don't much use the Brood summoner or the others.
Before talk about my magic formation of dragon + death, I'll say the others cards I use with Zintar that are playable for all:
Silent Sha-Vi, Undead Badger, Corpse Fiend, Death Elemental, Life Sapper. I lose a lot with this low mana deck in higher leagues, there is nothing to be done...
DRAGON
Brighton Bloom - Really good with Earthquake rule, I like to use with fire, since it also has fast destructive power.
Djinn Chwala - I like to use in low mana battles since Thorns does lots of dmg and Mylor Crowling is too expansive...
Drake - Usefull very few times, mainly only if the options are Fire or Dragon, I would peak Drake because the shield would be a great advantage in a melee x melee battle.
DRAGON + DEATH
Delwin Dragonscale - (+1 magic dmg).
This was one of the most strong formations I got for high mana battle:
For tanker it will depend if it is against magic or physical.
Bone Golem to tank against magic or
Harklaw against melee
Djinn Muirat Also a secondary tanker for both magic and physical with shield and Void Armor ability ,while also doing dmg with the help of Delwin.
Corpse Fiend and Life Sapper can also help here sometimes depending of the mana.
Phanthom Soldier - Does good dmg, has high hp, also to tank for back line, good speed and Flying ability.
Magi Necrosi - I found this one and the Camouflage and Snipe ability is a nice mix.
Insidious Warlock - With the help of Delwin, he gives 6 dmg every two turns because of Recharge.
Chaos Dragon - An super over power card, but with too much cost (14), its hard to get him into the field.
About prices, all thoses cards would be 6.4k CP and costing around 19.7 dec per day (for me at least). Around 325 CP/dec, not a good price since there are lots of legendaries and summoners.
I got luck on some rents making direct bids, also, break evens will depends how the dec pool distribution is, so try to make it in a safe way if so.
I rented now 100k CP for trying to get gold 1 EOS rewards, more three 20k CP gold foil cards, but didn't use any of them for climb. So it didn't make any difference on everything I talked before, besides them being somehow cheap because of low utility.
Good Luck there!!