RE: filler cards
Everything below the first 12 cards (4 purify, 4 holy light, 4 wings) seem like no-brainers to me (with one exception below). Wings i think is a good call, too, because we could lose an entire half of a deck (and we will, past round 1) and we could plug Wings into it, change mark to air, and have a working stall with pendulums. I think that is a great move.
Purify and holy light both seem too situational for me. I can see how they would have greatly increased utility when you know what color half your opponent's deck will be, but I still think they are too weak. Having near useless cards in your deck because your opponent doesn't poison could be fatal. And for holy light, well, it's a decent card, I just don't see us not having a better option.
At the same time, Rage Potions are great, but none of our decks really rely on them. They are one of the first cards I would have thought to stock up on, but as I look over our decks, I think we can do better.
So I propose:
-4 purify
-4 holy light
-3 rage potion (for a total of 3 filler ragepots)
-1 dragon
+4 chaos seed, which give the entropy deck a little survivability (with the cards we have, a first round loss would be rough. second round loss, it's definitely done.) with a few extra chaos seeds, it could at least survive beyond a loss, and i think at a later point in the war, it will be an even stronger deck. its extremely versatile and i think one of the hardest decks we have to counter. ascabi did a great job on it and i personally wouldnt have even minded seeing a second entropy duo.
worst case scenario, the entropy deck still loses, and we have a whole bunch of chaos seeds. with 3 rainbows + vreely's immodeck, though, chaos seeds have a home where they can still be very powerful. even if the entropy deck does well, 1-2 cost random element filler cards are not things we have extra of, and we could use some.
+4 earthquake
+4 lava golem
we are bound to have a deck completely fall apart. almost any deck we have now, though, could be converted into a fire/earth duo if it lost its current focus. earthquakes will be deadly throughout the war, and extra lava golems would round-out what would end up being a mono-fire with a splash of earth. deflags, fire shields, ragepots, dragons... any fire cards could be worked into it, and with earthquakes, it *always* has a chance. i think including these 8 cards would prop up a lost deck into a usable, unexpected, playable deck.
EDIT: if we get to a stage where we *have* to use all our cards or almost all our cards, 4 purify and 4 holy light are going to be hard to work into a deck. of the two, i am more worried about purify, as holy lights would still have a little bit of value in a rainbow even against a non-death non-darkness opponent.