At start i would want to add some armored mobs to the world. Minecraft armour wielded by skeleton/zombie could make it hard and more fun to play survival with friends. They could drop one damaged piece of their armour when killed. Of course there must be something very very new. I would add new weapons that can only be obtainable from mob that is wielding it.

Im thinking some purple weapons that all has their own special effects.

Dragonhead sword same as other minecraft swords but purple colour. 10% chance to instakill mod and 10% chance to deal 20% additional damage to other players. Chance that mob wields this weapon is 5%

Another weapon that im thinking could be Dragonhead longsword that is like 2 normal swords lenght and has 3 spikes both sides. Colour purple. 20% chance to instakill mob and 20% chance to deal 30% additional damage to other players. 4% chance that zombie uses this sword.

Also i would want to add Dragonhead arrows that are purple headed and they deal 20% more damage when shot to mobs and players both. It is 2% chance that skeleton shoots these arrows and when killed it will drop 10-20 of these arrows.

Dragonhead bow that fires only Dragonhead arrows it lasts 32 shots until it disappears. Dragonhead bow adds effect that when u headshot mob it will die instantly. 40% chance that skeleton uses this bow. Always uses Dragonhead arrows and when killed drops both of these (10-20 arrows).

None of these weapons can be enhanced.

Mobs:

Baby dragon

Small enderdragon that shoots fire balls that sets player to fire and does 1 heart damage while hit. Can fly 10seconds at a time and then 30 seconds on ground.

Drops:
(chance) (name) (amount)
100% 5 Levels of xp
100% Blaze rod (2-5)
100% Gunpowder (5-20)
20% Dragonhead sword
40% Dragonhead longsword
50% Dragonhead arrows (20-40)
50% Diamond armour piece
10% Dragonhead bow