Requires a civ that starts with Sun mana to build an adept, promote it with Sun I and waste a casting turn to use Scorch. Repeat the last step for as many tiles as necessary.
Requires a civ that doesn't start with Sun mana to research Divination, build an adept, convert a mana node (that could possibly be used for something better) to a Sun mana node, promote the adept with Sun I and waste a casting turn to use Scorch. Repeat the last step for as many tiles as necessary.
Neither of the above include the time it takes to even research to the point where you can build adepts.
Tundra can become plains.
Requires a civ that is neutral to research quite a ways through the tech tree to get Commune with Nature, build a Grove, train or upgrade to a Druid and waste a casting turn to use Vitalize. Repeat the last step for as many tiles as necessary. This may take extra work for Good or Evil civs so they can turn neutral.
Requires a civ to adopt FoL, research quite a ways through the tech tree to get Commune with Nature, build Yvain and waste a casting turn to use Vitalize. Repeat the last step for as many tiles as necessary.
Requires a civ that starts with Nature mana to build an adept, promote it with Nature I, wait for it to level up enough to upgrade to a Mage, promote it with Nature II, wait for it to level up enough to upgrade to an Archmage promote it with Nature III and waste a casting turn to use Vitalize. Repeat the last step for as many tiles as necessary.
Requires a civ that doesn't start with Nature mana to research Alteration, build an adept, convert a mana node (that could possibly be used for something better) to a Nature mana node, promote the adept with Nature I, wait for it to level up enough to upgrade to a Mage, promote it with Nature II, wait for it to level up enough to upgrade to an Archmage promote it with Nature III and waste a casting turn to use Vitalize. Repeat the last step for as many tiles as necessary.
Neither of the above include the time it takes to even research to the point where you can build adepts. They also don't include the fact that Nature I is only really useful for Elves or civs that waste valuable tiles as forests until the invention of the Lumbermill. They also don't include the fact that Nature II is completely useless for all neutral civs (which as is being discussed in another thread seems to be most of the civs in the game if RoK or OO spread enough). ANd lets not forget that neither of the above include the fact that Nature III is only useful for upgrading these tiles and once you have done that sufficiently, it is now a useless upgrade that you could have used for a more lasting useful spell.
Desert can become plains,
See the above section for a good part of this response.
Requires a civ that starts with Water mana to build an adept, promote it with Water I and waste a casting turn to use Spring. Repeat the last step for as many tiles as necessary.
Requires a civ that doesn't start with Water mana to research Elementalism, build an adept, convert a mana node (that could possibly be used for something better) to a Water mana node, promote the adept with Water I and waste a casting turn to use Spring. Repeat the last step for as many tiles as necessary.
Neither of the above include the time it takes to even research to the point where you can build adepts.
plains can become grasslands.
See serction 2.
Jungle can become forests.
Requires a civ that starts with Fire mana to build an adept, promote it with Fire I, waste a casting turn to use Blaze, wait for the smoke to become a fire, wait for the fire to go out, wait for the Burnt Forest to become a New Forest and then wait for the New Forest to become a Forest. Repeat step 3 as many times as necessary to remove all jungles.
Requires a civ that doesn't start with Fire mana to research Elementalism, build an adept, convert a mana node (that could possibly be used for something better) to a Fire mana node, promote the adept with Fire I, waste a casting turn to use Blaze, wait for the smoke to become a fire, wait for the fire to go out, wait for the Burnt Forest to become a New Forest and then wait for the New Forest to become a Forest. Repeat step 3 as many times as necessary to remove all jungles.
Neither of the above include the time it takes to even research to the point where you can build adepts.
Jungle can become grasslands.
Easier than the rest since it only requires researching Bronze Working but still requires numerous turns for workers to chop the jungle.
Lets also not forget that the Illians can turn useful tiles into Snow. And of course any civ with an adept with Sun I can turn a plains tile into a Desrt tile. While that has the same complications as section 1, it is still possible. Then there is Hell terrain. It doesn't occur in every game, or even most games, but it is another useless tile.
Now granted, all but mountain tiles can become useful tiles in some way, it takes work to do it and I think what many of the people posting favor is allowing this only for the two Dwarven races. Is this really so bad a suggestion?
Illians can use Snow, which is useless to all other civs. Malakim can use Desert, which is useless to all other civs and Infernals, while not actually able to use Hell terrain, find it more useful than all other civs because it doesn't hinder them and does hinder other civs.
I'm not saying that any of the above is a good reason to allow Dwarves to use mountains but to say that mountains are the only useless terrain in the game is a bit far fetched.