Currently in Minecraft there are potions that affect players and mobs and enchantments that affect items, so why not add spells that affect the environment?
To cast a spell, you need a lectern, which is crafted with a book on top and planks in the middle and bottom. You also need a spell staff, which is crafted with sticks in the middle and bottom left and a ruby* in the top right. To power a spell staff, right click on a lectern. That will open the spelling interface. It is similar to the interface of an anvil. Put a spell staff in the left slot and a spell ingredient in the middle slot. Then, take the powered spell staff out of the right slot.
To cast a spell, right-click on any block while holding a powered spell staff. Any affected blocks will then emit particles to show that they are under a spell. Spell staffs can only be used once.
There are two types of spells: Block spells, which affect blocks, and regional spells, which affect a region. If a block leaves a spellbound region, it is no longer affected by it. If it enters a spellbound region, it will be affected by the spell. Block spells will continue to affect the same blocks no matter where they go. Some blocks are immune to certain kinds of spells. For example, Redstone blocks are immune to the spell of gravity.
Here is a list of spells that I have come up with.
1. Power Spell. Ingredient: Redstone dust. The targeted block and the 15 blocks closest to it will act as Redstone power sources for a duration of two minutes.
2. Protection Spell. Ingredient: Shield. The targeted block and the 15 blocks closest to it will be immune to all other spells for a duration of two minutes. Useful for controlling which blocks other spells target.
3. Fertility Spell. Ingredient: Farmland. The plants that are in the same chunk as the targeted block grow twice as quickly for five minutes. Also, during those five minutes, blocks that are usually infertile (such as stone) can have plants grown on them. In addition to that, 50% more passive mobs spawn in that chunk. All neutral and hostile mobs are unaffected, except undead mobs, which only spawn half as much. Blocks of cobblestone have a 10% chance to grow moss.
4. Decay Spell. Ingredient: Rotten Flesh. Has the opposite effect of the fertility spell (plants grow half as fast, passive mobs spawn half as much, and undead mobs spawn twice as much). Lasts for five minutes.
5. Fire Spell. Ingredient: Blaze Powder. Sets the target block and the 15 blocks closest to it on fire, regardless of whether they are flammable. All fire burns out in two minutes.
6. Harvesting Spell. Ingredient: Diamond Hoe. All wheat, carrots, potatoes, pumpkins, melons, cocoa pods, logs, and leaf blocks drop items without getting removed, even if they aren't ripe.
7. Darkness Spell. Ingredient: Squid Ink. For two minutes, the targeted block and the 63 blocks closest to it have a light level of zero, even if they are in direct sunlight.
8. Strength Spell. Ingredient: Enchanting Table. For ten minutes, all enchantments and status effects will have twice their usual effect (if applicable) while in the same chunk as the targeted block.
That's all for now. If I think of any new spells, I'll add them.
Witches can cast spells. Bedrock is immune to all spells.
*Rubies are rarer than diamonds. If you don't want to add a new gemstone to the game, just use diamonds.