A Ghider Sight - The Ghider mini-boss.

The Ghider Sight is an event, which is caused by combining certain materials (let's say 3 diamonds, slime balls and blaze rods (this is just a suggestion, this can be changed)). In this event the fletching / blacksmith table is used to create a sort of item that summons. Only to be used during the night, throwing or using this item causes the players Minecraft to shake. After a while, a new mob (A ghast and a spider combined: 'Ghider') rises from the ground to attack the player. This is a mini-boss, like sea monuments, but on land and in the Overworld.

This mob, the Ghider, uses ability that allow it to harmfully attack the player like spitting fireballs and doing jump attacks (as normal in the spider and ghast). However, it can also call upon mobs like normal spiders and mini-ghasts to attack you as 'Minions'. This allows it heal and do more damage to the surroundings and the player. 

If the player defeats the beast BEFORE DAY, it is rewarded a prize of sorts (perhaps a lot of diamonds and good materials??). However, if the player dies or does not defeat the mini-boss when daylight arrives, then the boss despawns and life continues as normal. 

Multiplayer works similarly to all other bosses like the Ender Dragon.