This list is just my opinion and made mostly as a form of feedback so it only ranks the rulesets i have played, discussion is welcome.
S Tier
#33 - Trials stuff: Both players choose an element. In each deck at least 50% of the cards need to come from those 2 elements (note that your opponent may use your chosen element for that purpose as well).
Perhaps some recency bias here but i really enjoyed this ruleset, fairly nonrestrictive to build around and rewards prediction skill and analyzing the 2 element meta. Great on 20 upps to fit the trials theme.
#36 - TriPvP: Each player picks 4 elements, they may only use cards from those elements. Each player bans one of the 4 elements their opponent has chosen. The same combination of elements cannot be used more than once (mono/duo/trio count separately for this). If you use an element, you must use at least 4 nonzerocost-cards from it. Upgrades start at 0 and increase by 15 per game (so 0, 15, 30)
Another nonrestrictive ruleset to build around that rewards careful prematch decisions and prediction skills. The increasing upgrades takes this further as you have to decide what decks benefit from upgrades the most. My personal favourite
A Tier
#1 - Quanta cost of all cards in the deck must not exceed number of cards +10
Fun rueset that interacts interestingly with deck size
#4 - Trios G1, Duos G2, Monos G3, discord/eq banned
A simple dictation on deck type kept interesting by changing throughout the match
#22 - Only :gravity :life :fire :earth :death allowed. Marks from other elements not allowed. 15 upgrades (Upgrade number is optional).
This is the start of the trend where a simple restriction on only allowing 4-6 elements = A tier
#23 - Only :entropy :light :aether :time :darkness allowed. Marks from other elements not allowed. 15 upgrades (Upgrade number is optional)
Following the trend
#24 - Players have to choose between magic (:entropy :darkness :aether :time :gravity :death) or nature (:life :fire :light :water :earth :air) and can only use the element of their pick. Maximum 10 upgrades
Following the trend. This one is top of the bunch for giving a choice on which set of elements you play
#27 - A deck that has NO Time, Aether, Death, Life, Entropy, or Gravity cards. Only Fire, Water, Light, Darkness, Earth, and Air cards are allowed.
following the trend
#42 - Card Formation
Cards in the same column of your deck must all come from the same element. This order must be maintained after loading the deck code (the game automatically puts cards in a certain order).
The suggested 12 upgrades make building for this ruleset fiddly and interesting
B Tier
#9 - All creatures/permanants with an active ability are banned.
Interesting idea. Really needed a cardlist for banned cards
#25 - At least 50% of the cards must be from one element.
A fine ruleset but a missed opportunity by not making players announce 2-4 elements their decks would consist 50% of before the match
#28 - Only duo decks allowed, though they may not consist of opposite elements.
Could be just me but i mostly play and play against duo decks so i feel this ruleset dosent add much
#37 - Reverse Ranking:
(https://i.imgur.com/MaEbBix.png)
No real thoughts just feel it fits in B tier
C Tier
#31 - Deck size has to be exactly 40 cards, no permanents (other than pillars/pendulums) are allowed. Firebolt, Icebolt, Drain Life are banned.
Forced 40 card decks. YIKES
#32 - (https://i.imgur.com/dK1nnsn.png)
#35 - Double trouble:
(https://i.imgur.com/9wqA5kM.png)
The meta is fine, i saw a nice variety of decks, I just feel this style of rule is much better suited to a tourney
#39 - Poor man's shinies:
(https://i.imgur.com/QKLcWqj.png)
This is perhaps unfairly placed in C tier simply because the cardlist for cards that can be used upgraded shows the unupgraded versions
#41 - Original Card Do Not Steal
Each player announces a card before the match (if you want to make sure that there is no advantage to waiting, get a random person in chat as arbiter and pm them your choice (your opponent should pm the same person); once they got both the choices the arbiter will anounce them publicly).
You have to use at least 3 copies of your chosen card in each deck.
Your chosen card is banned for your opponent.
Not sure how i feel about this one, perhaps pillars/pends should not be allowed to be chosen. 1 card for the whole match can be rough
D Tier
#38 - Hyperdimensionsional sideboard:
Instead of changing decks each game, you may only change up to 15 cards after each game (these changes can be substituting a card with any other card (=replace with another card) or removing/adding a card). You may change your deckmark any time for free.
Did not like the restriction on being unable to freely change deck between games
#40 - Dalek's Extermination Fit:
(https://i.imgur.com/S1fIuzS.png)
Kinda just hated this ruleset