The question should really be FK now or wait until SDE:L for ??? time and ??? $$$ (not sure they have a retail MSRP yet). SDE 1.0 is really just buying minis that will be reprinted since much of the game content was replaced with FK anyways and FK has far fewer components that are replaced by 2.0. FK will unlikely have any more copies printed in its current incarnation since the rules are replaced by 2.0.
Also, FK is listed on the online store, but is out of stock, but I think it's on amazon for $107 prime shipping, which is quite good considering how big/heavy the box is.
We don't know the SDE:L 2.0 classic or arcade MSRP, but they will have fewer minis than SDE 1.0 or FK in terms of entry point.
I highly recommend FK for the minis, but not the ruleset, and there is some work you need to do to use the SDE 2.0 rules so you'll have to decide if the additional effort will be worth the time vs. just waiting.
FK comes with:
5 heroes
2 single spawn points, 7 monsters + 1 spawn, 16 models total -- 2 alternate profiles available
1 linked spawn point, 12 monsters + 2 spawns, 14 models total -- 2 alternate profiles available
2 mini bosses, both can be played as heroes
1 dungeon boss
6 pets - compatible with Pet Parade, but need to use the new profiles
6 creeps - compatible with Pet Parade, may also be used as a pet
*Treasure chest and boo booty models
6 double sided dungeon tiles compatible with 2.0 - SDE 1.0 tiles are a diff. size and don't have proper tile effects
Counters compatible with 2.0 -- the only things you are missing are activation counters (I use keys) and Immobile (new, official status effect - I use skulls in arcade b/c there are many options) - SDE 1.0 counters are not compatible
Loot deck - mostly compatible with 2.0, there are minor balance changes
Treasure deck - mostly compatible with 2.0, there are corrections and minor balance changes (pets are no longer treasures)
*These are not included in 2.0 - counters are used instead
To play FK /w 2.0 classic you need:
1) SDE 2.0 classic rules
2) SDE 2.0 classic Mighty Monster Chart (MMC) & backpack
3) (opt) Add/update to 2.0 Classic loot cards
4) (opt) Add/update to 2.0 Classic treasure cards
5) Use proxy tokens for Immobile (crystals) and Activation (i used keys)
You can play 3 to 5 hero classic games. 6 hero games require you use a mini boss as a hero, but you also need 2 mini bosses.
Pets and creeps are not used. This is the lowest effort to use 2.0 rules, but is pvp.
To play FK /w 2.0 Arcade you need:
1) SDE 2.0 Arcade rules
2) SDE 2.0 Arcade Mighty Monster Chart (MMC) & backpack
3) (opt) Add/update to 2.0 Arcade loot cards (2.0 Arcade loot is based off FK loot)
4) (opt) Add/update to 2.0 Arcade treasure cards (2.0 Arcade loot is based off FK loot)
5) Use proxy tokens for Immobile (crystals) and Activation (i used keys)
6) SDE 2.0 challenge & boss challenge cards
7) SDE 2.0 plot cards
You can play 3 to 5 hero arcade games. 6 hero games require you use a mini boss as a hero, but you also need 2 mini bosses.
Pets and creeps are not used. This can require quite a bit of printing for the challenge and plot cards, but is pve, and some folks have digital solutions rather than print stuff out.
Pet Parade is two parts - pets and creeps. To play pets you need:
1) Pet Parade rules
2) Pet cards
Pets make the game easier for the heroes at the cost of increasing play time. But pets are super cute.
To play Pet Parade Creeps you need:
1) Pet Parade rules
2) Explore Consul Plot Card
3) Arcade Challenge Card
4) Arcade Plot Card
Creeps add a lot more flavor to the game, especially for Arcade Plots, and can add a lot of minis to the board and thus can extend play time, but appear to be balanced around having 12 creeps (as per tile packs) per plot and challenge so 6 squirrels may often be insufficient to cover all the creeps you may normally need except in some 3 hero/tile games.
Still, there must be something to be said about trying to avoid and/or defeat the squirrels so they don't invade your pants.
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for me, to print the arcade MMC/backpack, core cards, pet parade cards on nice card stock cost ~$50 (b/c i wanted free shipping) at staples. Other folks have been able to do it much cheaper for ~$20. So that's an added expense if you print, but it can also be a nice project if you want to do something together.
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Waiting on SDE:L will most likely:
1) Wait an unknown amount of time for a product with no set release date for ks delivery or retail (assume SPM will share dates once they can guarantee them)
2) Let you pick SDE Classic or SDE Arcade to better fit what you want to do -- TBD if this will cost less than FK due to lower # of models.
SDE Classic and SDE Arcade only let you play their specific mode out of the box, but you can still print all the preview rules out to play the other mode same as FK.
The big difference is you'll have fewer models and thus can't play 5-6 hero games w/o getting more minis/proxies and wont' have pets/creeps
6 heroes (1 more devoted hero, no mini bosses that can be played as heroes)
3 spawns worth of monsters (-1 spawn worth of monsters, but they will also have alternate profiles)
1 mini boss (cannot be played as hero)
1 dungeon boss (Arcade Boss has Daemonus, so actually 2 models

)
Treasure chests and boo booties are now counters
No pets or creeps models
**Don't have to print anything extra, but you CAN still do so to play the mode you didn't purchase and Pet parade.