You cannot activate these effects in the same Chain
The key card to the archetype's resource loop is their Field Spell "Runick Fountain", which lets the player activate "Runick" Quick-Play Spells from the hand during the opponent's turn, and once per turn (during either player's turn) it can place up to 3 "Runick" Quick-Play Spells from the Graveyard to the bottom of the Deck and have the player draw that many cards
Jumbo Cactuar is a 1/7, which gets a +9,999/+0 buff when it attacks
When it was banned, Wizards cited the reason for its banning as being poor color representation for red alongside the UR Twin deck taking up a large enough portion of the meta (around ten percent) that it was barring other deck strategies from having a proper chance
Keep in mind it does say cast a spell, so anything is on the table besides lands
Lets start with the colorless Eldrazi cards, as they come first in number order