You check the label and realize it actually says “Tenser’s floating Dikc”, but the salesman is already gone.

Arcane Dye - for when you don’t want to worry about mixing your whites with your reds.

Healing Ward - blocks all heal effects on the target.

Heap Metal - for when you don’t feel like paying a hireling to collect the gear of that bandit camp you just slaughtered.

Antilife Spell - wait, I guess that’s just Power Word Kill…

Burning Lands - when Fireball just isn’t Fireball-y enough for you.

Chromatic Orc - summons an orc ally. A different color each time you cast the spell.

Control Hater - a more powerful version of Command that only works on things that are currently hostile to you.

Fire Stork - that wizard must have really hated storks. Incinerates the nearest stork.

Fig Cloud - an alternative to Hero’s Feast for vegan parties.

Glyph of Barding - acts as armor for your horses.

Prismatic Ball - hold on, I’ve been notified this was just a mistranslation of Chromatic Orb. Never mind.

Rope Brick - this is what you get when you let the Barbarian make spells.

Sheep - conjures a sheep.

Stonespin - does what it says on the tin.

Runbeam - force the target to move their full speed every turn.

Rime Stop - I was kicked from a table after bringing this into a Rime of the Frostmaiden campaign.

Wash - why would you spend a 9th level spell on Prestidigitation?

In my eyes, the Rule of Cool is best used as the opposite of the Air Bud Clause. (For those who don’t know; the “Air Bud Clause” refers to a rule in basketball that basically says “it’s not allowed just because there’s no rule against it”.) TTRPGs are imperfect systems, and you are going to run into a scenario that isn’t covered in the rules. Rule of Cool is best used here, rather than to bypass rules that do exist.

But also; some systems can be really crunchy, and a lot of the time it can be more fun for everyone involved if you just say “you know what, that’s cool, let’s do it” than to pause for five minutes to leaf through some rulebook (because seriously; you can’t always know the entire rulebook by heart) trying to determine if and why they can’t.

Of course, doing this too much is dangerous. Hence “in moderation”.