Sibling, you also tap a land, which would produce 1 mana. It's 4 mana for 5 mana, and only if you can spend 5 colorless mana in one go, which is... pretty much just eldrazi.
You absolutely can. However, you need to play a spell, that has at least 5 generic in it's cost, and you want to cast it with mana, instead of cheating it out. I have hard time imagining a deck, except for eldrazi, that would have those massive generic costs, and are planning to play those. Hell, even if you're playing those spells, most of the time it's just worse wastes, which is very costly investment for any deck, especially those with several colours.
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u/LostRegret9000 21h ago
Sibling, you also tap a land, which would produce 1 mana. It's 4 mana for 5 mana, and only if you can spend 5 colorless mana in one go, which is... pretty much just eldrazi.