The best way I've seen to defeat an enemy without killing it is Flesh to Stone, Stone to Mud, Purify Food and Drink, and then boil the water away. That was more for keeping an enemy from being resurrected, but it would be a cool overkill way to get rid of a tarrasque without using Wish.
And without a burrow speed, and without a ranged attack, and without an ability that lets it ground all flying enemies. Maybe a skilled DM could make it work, but in other editions it wouldn't have been an issue.
Though the other problem is that you can deal limitless damage just by dropping sufficiently many 100 pound boulders. In 5e, they got rid of damage from falling objects, but you just need to drop enough creatures. Or ignite enough horns of gunpowder with a single Bonfire.
I've been thinking it would be cool to have a campaign set after the town has gotten smaller. You go on your first mission to fight a cave full of kobolds or some such, there's an earthquake that blocks the exist, and you have to fight through it and escape before later tremors cause it to cave in. It's fairly standard, until you leave, and find out what was causing the tremors. At some point decades or even centuries ago, the rate they dealt damage to the tarrasque dropped below the rate it regenerates. Then it spent all that time slowly losing the nonlethal damage, until finally it was enough to regain consciousness. The city is left in ruins, and now the nations of the world have to deal with the tarrasque acting like a roving natural disaster. Maybe at the end, you have a choice to rebuild Salt in the Wound and get that source of alchemical supplies back, or kill it for good as the only way to be sure this never happens again.
Simply containing each number sequence is a significantly weaker property than having them all occur at the right frequency. Still, while nobody has proven it, it's generally expected to be true.
Figuring it out on your own is science, but I have a feeling OP didn't actually personally search the world for one-horned horses or pointy eared-people with long lifespans. I bet they didn't even work out how biology changes with scale and how evolution works to show that there can't be tiny winged people.
Fun fact: a level 14 Creation Bard can create a loaded antimatter rifle. Arguably, they could do it at level 3. Since it doesn't have a value, it certainly doesn't have a value of more than 20 times the bard level in gp. The problem is that it's not clear if you can count that as one object.
Also, Creative Crescendo mentions channeling power from the Song of Creation, but nothing about actually singing it. And it's not a spell with a verbal component. I see no RAW reason you wouldn't be able to use it by miming.
Lesser Restoration is a level 2 spell that tons of classes can cast and has no material components. Getting cured of the horrible blood plague isn't that difficult.
Also note that a mounted character can travel at twice the top travel speed for an hour. It doesn't specify anything about what creature they're mounted on. And with the right feats they could be helpful. Imagine a tank with a Mounted Combatant feat riding the squishy wizard and absorbing all the attacks against them.
The best way I've seen to defeat an enemy without killing it is Flesh to Stone, Stone to Mud, Purify Food and Drink, and then boil the water away. That was more for keeping an enemy from being resurrected, but it would be a cool overkill way to get rid of a tarrasque without using Wish.