Dalk severely underperforms compared to other legendary heroes - especially those that are tagged as "Defense" - Dalk is a unique RANGED defense type, which means you can use him strategically to force a boss to move to his position... but his skills are very confused and mishmash of attacker and debuffer but not defense related at all. So please consider these suggested changes...
#Adjust Dalk skills for balancing
strange bloom
Passive: Instead of the just the attack penalty at start of battle that fades away after 30 seconds (clearly intended as an arena focused skill)... move the Banish effect from his ult to the passive. This would mean the start of the battle the highest attack unit is banished for 5 seconds AND attack down that fades away... make the attack down effect start when the banish ends... Since banish does not stop the generation of ultimate like other sources of control (stun, frozen), this is a strategic use of the unit to debuff the enemy for what will be their first two quick actions upon coming back from being banished: battle skill and ult almost immediately together. This might be a double edged sword in that back to back skills can be very painful, but the passive attack down for 30 seconds stacked with a timed attack down debuff on that unit could prevent catastrophe. This keeps the passive focused as an arena skill and helps in dungeon/boss fights for the first 30 seconds by reducing attack a bit (that stacks with the attack down II debuff).
Battle skill: Currently Attack Down II single target... this is ok and in line with what some other defense units do... except that it is almost identical to Horrus (epic unit...).... but slower.
Horrus battle skill is 75% attack down II with 5s initial and 10s recast, single target with a defense% stat modifier for damage... Dalk on the other hand has a 7s initial, 12s recast single target 100% attack down II.... with an ATTACK% modifier? what kind of moronic design is that for a "defense" unit...? he's basically worse than Horrus comparing battle skills.
Eurion... has an AOE 3x3 square, DEFENSE% BASED DAMAGE, 5s initial, 10s recast, 100% attack down II that first DISPELS ALL SHIELDS? again... how do you even compare that to Dalk's trash battle skill?
My suggested change: Lower the timers to be 5s/10s after skill scrolls; change attack based damage to defense based; make it area effect like eurion's... but additionally make it a 3x hit rather than adding an additional effect. this will make Dalk actually be able to deal decent damage with his battle skill. Keep the timer at 5s for the attack down debuff so it is not too powerful.
Ultimate: I think the accuracy bonus 50% buff for 10s he gains is an absolute waste of a bonus for a legendary defense hero... you build tanks 4000 defense with 200 accuracy very easily, which is sufficient to debuff just about anything in the game reasonably with affinity bonuses added on top of those stats... adding that bonus on a defense unit with no other self buffs is pretty useless. I suggest instead to dispel all debuffs to the hero himself + add Defense Up II for 10s to himself (similar to Bionphray)... These two effects should take place prior to the damage, which can remain single target so it is not too strong... but the 820% damage modifier needs to be changed to Defense% not Attack%... keep the ultimate reduction at 30%.
If you look at him currently... he basically does what Vinyara does almost exactly... except way worse. Instead of Frozen, he Banishes... instead of 100% ultimate energy reduction(!) he only lowers it by 30%... Vinyara also applies attack penalty II for 10s with her ult - and that is AFTER she removes all the enemy buffs!!! what a great ultimate for a legendary hero... except she is support.
Dalk needs a serious rework of his ult to be effective and comparable to other Defense and Support legendaries... so to repeat:
Ultimate: Dispel all debuffs on the hero first, apply Defense Up II to the hero, then single target damage (820% defense modifier) + 30% ultimate reduction.