The Ur-Ghast from the Twilight mod. Lets say its the mother of all ghasts. You can find it on top of the gigantic Dark Towers.
The Ur-Ghast will be hard to defeat it will break any armor fast if they are not good the ones you need to use are the Steel Leaf armor and Naga Scales armor are the armor you need. Use Salamander's Eye to reflect to projectiles.
The Ur-Ghast has 250 health, it will shoot fireballs direct at you (direct hit). The tears that the Ur-Ghast makes does 1 and a half hearts and don't use the Frost Bow it will not slow it down. This boss will stalk players and then will attack you but, it too big you can see it stalk you you know it's very big and all. To help kill it also download some mods. It will be very easy for you and if you don't its ok you want to make it challenging.
The Ur-Ghast will summon little Carminite Ghastlings with a lighting strike. The Ghastlings will spawn it ghast traps. This trap is set off by a redstone signal and sucks in nearby Ghasts when powered. To power a trap, the player must slay 2 Carminite Ghastlings near it then activate the block via redstone signal. This will cause a musical pulse, which gets faster per Ghast death. This can draw in the Ur-Ghast to range of a melee weapon. It is destroyed most quickly with an axe.
When low health the Ur-Ghast reaches tantrum mode, it will just keep spamming minions to attack you. It wll also change the weather. The Ur-Ghast starts attack you and start screaming and also cries ghast tears that does 1 and a half hearts and you can't pick up the ghast tears.
The Ur-Ghast destroy your armor very quickly.