I won't go deep into each one, but they all have some form of cycling which can be a boon if drawn later in the game when you don't need them, or, of course, for cycling strategies (toss in a Fluctuator and burn through your whole deck.) Some produce colorless or single-color mana
Luckily Rise of the Varmints does not have flashback
The Bloodsky Massacre is a powerful saga within BR Limited and tribal Berserker Standard builds
Some older options include Mentor of the Meek and Garruk's Uprising, though these may require a bit more effort or specific conditions to draw a card
Imotekh the Stormlord Imotekh the Stormlord asks that you build around artifacts, much like the rest of the Warhammer 40k necron commanders
Complicated math problems aside, the challenge is well worth it