They are meant for the game permanents that dont change out like a Commander (MTG), Sorcerer (Sorcery), or Hero/Equipment (Flesh & Blood)
If you have a consistent enough plan to get your win the game cards out regularly, you can reduce the number of copies of those cards and run more counter magic to protect yourself and your combo
Panorama lands are another budget-friendly option, as they offer partial tri-color fixing by fetching basics
While goblins are undeniably iconically red creatures, its hard to consider the expendable little weirdos the best. Goblin Recruiter is the best solely because it can tutor up every other good goblin all at once
They can't be the target of spells or abilities, their static abilities have no effect on the game, their triggered abilities can't trigger, they can't attack or block, and so on
The most literal are cards that make your second spell cheaper, like Monk Class and Alisaie Leveilleur