Swain isn't working as intended.

Swain is being played as a support atm, he is an ok support, but he is not meant to be a support, he is meant to be a Juggernaut carry.

Riot said so themselves, that he is meant to be a warlock juggernaut was their words.

Can he duel darius/garen/fiora/insert-juggernaut/ANYONE whilst having superior farm in melee range? If the answer is no or not even close then he isn't working as intended.

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My suggestions.

Q - Rename Eldritch Destruction (More Classic D&D Warlock name Eldritch Blast)

Reduce base damage by 50%, reduce scaling by 50%, Reduce Mana cost by 50%.

Make instant cast, make it a channel you can use whilst moving, so it is like a constant channeled lightning. The channel ends and the cooldown starts when you let go of the button (or press again if you don't have quick cast on)

Gain a soul shard every two CONSECUTIVE UNINTERRUPTED seconds you channel this and hit one or more enemies without interruption (so if you drop it at 1.5 seconds you'll need to start again)

W - Dark Discorporealization (Classic D&D legendary warlock ability) 25 sec cooldown (not reduced by rank)

Burst into a flock of ravens made of darkness for 3 seconds, radius 700, damage 100/150/200/250/300 + 50% AP.

Untargetability, gain 40/45/50/55/60% movespeed for 3 seconds.

E - The same except you can press E again to detonate mid-way.

Ultimate -

Increase duration by 1 for each soul shard. Increase per second Damage/Healing by 10% for each soul shard.