ItemSorcery
This small plugin adds six spells to the game:

• Slowness: puts a slowness effect on the affected entity.
• Push: pushes the entity in the direction the spell caster is looking.
• Drowning: summons a rain cloud over the affected entity, it will drown them causing one point of damage every half second.
• Explosion: causes a small explosion where the entity is standing.
• Jump: sends you moving toward the direction you are looking.
• Freeze: freezes water.

Each spell costs a configurable amount of mana to cast, and the maximum amount of mana a player can have as well as the rate at which their mana regenerates is also configurable. The mana is displayed above the player's hotbar when they are in a state whereby they can cast a spell.

The way a player can cast a spell is by holding a particular item in their off hand while keeping their main hand empty and then simply right/left clicking at another entity. Note: the freeze spell cannot be used on entities, only on water blocks. So to use the freeze spell you must look at water within twenty blocks of you.

• to cast a slowness spell, hold a soulsand block in your off hand and keep your main hand empty
• to cast a push spell, hold a dirt block in your off hand and keep your main hand empty
• to cast a drowning spell, hold a water bucket in your off hand and keep your main hand empty
• to cast an explosion spell, hold a tnt block in your off hand and keep your main hand empty
• to cast a jump spell, hold a rabbit's foot in your off hand and keep your main hand empty
• to cast a freeze spell, hold an ice block in your off hand and keep your main hand empty

Each spell can be enabled/disabled in the configuration file and the mana cost of each spell can also be changed too.