In GameMode X the night may be harder then the normal Vanilla Night. Every X days (currently 15 days) a event will be triggered when the night its the overworld. You will be warned of which event is running. Some may be world events others may target a random player.
When the Blood Moon is triggered, every mob will receive a buff, the same buffs has they receive from Enderman Support, but instead of only around enderman, this will happen around the entire world.
The amount of mobs will also duplicate. So you will have to fight double the mobs you would normally have to. This will also increase the chances of champions spawning.
Note that you wouldn't be able to sleep during a blood moon and the blood moon will only end at daybreak!
When the Zombie Hord gets triggered, a random player is choosen, when found a horde of 10 random zombies will spawn around the player position and start attacking.
This is dangerous, however, using a Mob Unspawner in your base will prevent the horde from spawning, so you will be safe.
Different from the blood moon you can sleep during this event, it is a single time event, so it will only occur the moment it is triggered.