Mastering the Cards Shard of Serendipity, while it is my favourite card, is not as versatile as it might seem. Most of the time, if you plan on using this card, you can't really use any other entropy card except supernova, unless you plan on packing tons of entropy pillars as well. Having said this, this card is best used in rainbow decks with quantum pillars and supernova in them, or, if you're crazy like me, in mono entropy with supernova. While not being very effective unupped, this card can become great when it is upgraded. Drawing three upgraded cards with a single one for three entropy quantum is a really good deal. Of course, there are times when you can get unlucky and get some pillars, but those cases are pretty rare considering the pool of cards available, which is every card in the game except mark cards, nymphs, shards and Miracle. The cards that work well with Shard of Serendipity are Supernova (not that great with nova), Quantum Pillar, Bonewall (You can get good spells out of Shard of Serendipity to supply your bonewall), Flying Weapon (There are also a lot of weapons, and this helps making them useful rather than clogging your hand) and many others. So if you plan on using this card, keep in mind the cards and the types of decks I mentioned.
Nova is one of the most versatile and most used cards in the entire game due to its ability to give you a burst of quantum in the early game, allowing you to rush your opponent with cheap and powerful cards. Nova is best used in decks that use cards from all elements, but the total cost of cards for a single element should not exceed four, unless they match your mark's element. In nova decks it's usually recommended to use a few quantum pillars as well to make sure you have a continuous quantum generator. One of the most famous decks uses this card: the Grabbow, also known as Antabow due to the creator's name: Antagon. The cards that work best with Nova are Graboid (cheap creature that most of the time deals at least 10 damage), Forest Spirit (Nova allows you to play this early and grow it before your opponent can deal with it), Arsenic (great value for its cost) and Fog Shield (considered one of the most broken cards in the game due to its ability to do so much for such a low cost) and pretty much any 1 to 4 cost card in the game.
Supernova is actually more powerful than its unupped counterpart, even though it might seem weaker since it costs two entropy quantum to get it played, it allows you to play cards that cost a lot more, giving it a lot more versatility. With Supernova you can use 1 to 8 quantum from a single element, giving you access to cards that Nova decks can only dream of. Supernova is best used in decks that use entropy mark (although it can be used with entropy pendulums and a mark from a different element), a few Shard of Serendipity, several Quantum Pillars and a few cards from each element. One of the most famous decks that use this card is the Loufoquebow (or however your spell that). The cards that work best with Supernova are Shard of Serendipity (you will end up having a lot of spare quantum, especially if you also use Quantum Pillars), Bonewall (having Supernova allows you to use expensive and powerful CC cards as well), Pulverizer (PC on a stick, usable several times in a Supernova deck) and pretty much any 1 to 8 cost card in the game.
To sum up, Nova and Supernova might count as the same card, but they are used in completely different decks, so keep that in mind when you want to build one of those decks.
Discord is a very powerful weapon that allows you to potentially win a game with your opponent unable to do anything at all during the whole game. Quantum control is a very powerful aspect in Elements the Game and a very limited one as well. Even though this card was slightly nerfed by reducing its maximum scrambling capability, it is mostly irrelevant to its purpose. Discord is best used in decks that want to win as fast as possible or in some slower denial decks, but it is also usable in midrange decks, though it's almost completely useless in stall decks. One of the most popular decks (and generally not fun if you're on the receiving end) is DBH, which stands for Discord-Black Hole. The aim of the deck is to play Discord early and when it seems like there's nothing more to scramble from the elements your opponent needs, it uses Black Hole to absorb all the scrambled quantum and the cycle starts all over again, and during this time chipping away your opponent's hp with cards like Abomination, Saphire Charger or plain Purple Dragons. The cards that work best with Discord are Black Hole (stated above), Earthquake (similar to black hole, but instead of absorbing the scrambled quantum, you deny their useful quantum directly, leaving them with useless quantum), Devourer (Similar to Black Hole, but it can be played quicker and it also acts as a quantum generator) and many other cards. If you plan on using Discord, keep in mind the deck and the cards I mentioned.