Radiant Greninja will help you with its Ability, Concealed Cards , which will force you to discard an Energy card from your hand but, in exchange, will let you draw two cards from your deck
You see, you get to draw a card for each Creature you control, which is good, but you also gain four life for each Creature you control that has four power or more
330 HP is a massive tank that wont easily get KOed, 1 Energy attacks are always great, and doing 220 damage for only 2 Energy isnt bad either
Kroxa provides low opportunity cost inevitability to these decks, allowing them to win grindy games, which is key to giving Rakdos decks that bit of extra texture that sets them apart
Predicting the next Magic bans can be a tricky business these days
Plus, being Grass-type, one would be forgiven for assuming both cards match the role