The Fallen Kingdom’s Fire / Dark faction is a combo deck about death and destruction. Willing to do sacrifices for destruction power.
Fallen Kingdom tries to fill the board with undead to setup big turns.
The deck is basically composed of cards that enable you to sacrifice resources so that you can perform powerful offensive moves, or reward you for sowing death.
Fallen Kingdom incentivized to be aggressive and put pressure on the opponent. Aggression and pressure generate an exchange of units, that means death, and that is where the Fallen Kingdom is at its best.
A game state where the interaction is high, is where Ret-Talus can do explosive combos. His main strategy is to setup both the board state and his hand in such a way that he can either fuel a massive Sacrificial Pyre, imbue Undead Warriors with monstrous attacks or generate a path of fire that leads to a direct assault on the opponent’s summoner … and why not all three?
Fallen Kingdom's biggest strength comes from Ret-Talus himself. His ability is economically very strong, but more importantly it generates strong tempo, reviving an undead warrior is a card gain of 3 magic. One for the card you save and two for the magic it costs. That means that while other decks are drawing 5 cards, you are “virtually” drawing 8 in addition to ensuring you always have a common unit available. That is very important because it means you don’t need to keep a common undead unit in hand even if you feel you may need it because Ret can always get one from his discard pile. This is especially critical because with a heavy combo deck like Ret-Talus’, hand space is at a premium.
Ret may not prefer it, but he can play a slow game if needed. When Ret is played more slowly, it allows for more time to build up a good hands to create a better combos.
Fallen Kingdom has two very difficult decision points, hand management and Ret-Talus positioning.
Ret’s biggest weakness is his lack of range. It may not seem obvious as he is ranged himself and he has 2 ranged commons. Yet neither he nor his commons actually fare well in ranged combat. So Ret needs to put gates as far forward as possible, or work as a gate himself to help keep the enemy engaged in melee, or he will be easily outmatched.
So overall, burn your magic aggressively, Raise the Dead a lot with Ret, summon a lot, use your movements every turn and try to push as far forward as you can, without exposing yourself too much. You may need to take some calculated risks, just don’t get reckless. Your strength is mainly in tempo and it's okay to sacrifice some economy to keep your tempo going.
If you have more magic than you can invest in commons, it's not time to slow down, instead it is time to start bringing the champions in. You have only 3 movements and 3 attacks and the best way to take advantage of such is to bring in high-damage champions.
Once you are maximizing your three moves and three attacks per turn, and have a champion out, then maybe it's time to slow down a little to try to build that hand for a massive Sacrificial Pyre turn. If you manage to build a huge pyre in the chaos you are hopefully creating, you probably will win.
They do have some economic tools in the form of Undead Carrier, Blood Summon and especially Sacrificial Pyre, but it's an economy that is more intended to keep the pressure on without running out of gas, rather than one that allows them to play a slow, "grindy" sort of game. They are instead rewarded for playing a highly interactive game, forcing constant contact with the enemy.
You can win through your economy if you can pull off massive Sacrificial Pyre turns, but more often than not this is only achievable by being so threatening that your opponent is forced to respond defensively to your aggression. Thus, winning through economic advantage is more of a Plan B, than it is a consistent path to achieve victory.
This faction is not for the faint of heart or those that like to play it safe, since playing them well means living with a summoner in a constant risk of dying and making often inefficient economic plays for the sake of board position.
However, if you enjoy having to make risky positional plays, tough decisions and trying to shift the board state and your hand into an explosion of death, the Fallen Kingdom may be the most fun of all.