Which Legendary to build

[Panda Tar]

Yeah, just like my Dracolich getting its 25% status resistance, which I still haven't swaped.

[Nelar]

Desolator

[Pol]

Desolator is not so much great. It's dungeon boss with weakness. Like Phoenix, both can be beaten easily.

[Panda Tar]

The most all-around Legendaries are not numerous, those we can use both for battle and as dungeon bosses. A few that comes to my mind are:

• Cerberus: decent multiple damage ignoring defense, inflicts Dots, heals itself for each inflicted Dot, counterattacks with 1 stance of Special Attack (meaning it can inflict Dot and ignore defense, and I am not sure of this, but I think this case specifically ignores the On Death enemy ability, if Cerberus kills with this special retaliation). I like Defender tome or Brawler to this one. Good vs less enemies, given its bites are random.
  Stegosaurus: attacks the row and breaks their defense. A 4-dot one with Defender tome is nasty to deal with. Good vs few to multiple enemies.
  Ceratops: attacks all targets multiple times, buffs itself and can stun for 3 turns. Enough for it to come around and use Special Ability again. Also has a lot of resistances to statuses and damage. Good vs few to multiple enemies.
  Dracolich: attacks all enemies ignoring defense based on its own HP, heals, has status immunities, has resistance to damage and one dispel. Good vs multiple enemies, but not very good 1 on 1. I like using the tome which grants greater HP. Enchantmens I would recommend bonus HP, bonus damage vs Large and Boss, maybe double strike.
  Colossus: hits all enemies, may stun, dispels multiple buffs and ignores defense. Aside form self-sustaining, it is basically a badass boss. Good vs few to multiple enemies. To have it sustaining, perhaps a Defender Tome, and at least enchantments that improves Def when HP is lower, bonus damage vs large and boss, maybe heal self when killing enemy, bonus critical damage or crit rate.
  Medusa: multiple hits, although part is random, has a very powerful stun. Fully awakened grants Special hits to always inflict critical. That being said, a good combination for sustain as a boss might be Defender tome (which heals back life whenever inflicting critical hits) and enchantments that grants higher damage vs large and boss and bonus damage for critical strikes. Maybe a PWR boost as well.
  Sandworm: attacks a row, multiple stuns. If one enemy on the line is already stunned, it will try to stun everyone again. Decent damage, some damage resistances and self-healing when killing an enemy. Good vs few to multiple enemies, even having a sustaining based on "on kill", because it also stuns.
  Fallen Angel: massive single damage which will undoubtely kill someone. Whenever it kills a target, it will heal itself and inflict a decent amount of damage on all other targets. It also debuffs the target with Fatigue. It the target is already debuffed, debuffs all other targets. Without anything to cleanse that, it will be difficult to heal back. As its sustaining comes from "on kill", it is good vs single to fewer enemies, enough for it to heal when more than one, given one on one will be a single-blow kill. Vs too many enemies might not be very effective. Enchantments regarding sustaining should be considered.
  Behemoth: massive random multi damage strikes which might stun and dispel. Very high natural HP and DEF, which can be effective couple with healing-focused Tomes. It is a very hard boss to take down when 4-dot and not controlled.
  Monkey King: multiple chained damage which bounces and get stronger at each bounce, it is specially good vs 2 or 3 units. Not good vs too many or 1 on 1. Probably giving it a proper Enchanment combination can make it scary.

These suggestions for tomes or enchantments are thinking more on the lines for Dungeon Boss.