Disable Sona on ARAM
This champion is oppressive on ARAM. Ever heard of Sisyphus ? Every time I get matched against a Sona in ARAM that is how I feel.
When she is on my team, it's hilarious. I can recklessly dive at level 3 because i basically have infinite health thanks to this champion; it feels like bullshit and i know it is, but it's hilarious. When she's on the other team, you experience the direct opposite. You may occasionally get lucky and have a hard engage team against a Sona without tanks, but unless that unlikely scenario occurs, you just lose. Straight up. No counter play, you just lose. Harass and poke is irrelevant because with the increased mana regen on ARAM, SoNa (yes she brings out the salt in us ARAM payers) has infinite mana which translates into infinite health for her team.
Her meaningful weakness in Summoner's Rift of a squishy support who must put herself at risk in order to land some harass completely flies out the window on Howling Abyss. Why? Because it's a 5v5 and there is a tower mere teemos behind her. She doesn't have to put herself into those risky situations since she has 4 members who can lay down the harass while she sits back and spams infinite health for her teammates. They can lose trades HARD, and yet they in fact win those trades because then they can sit back and heal up. Meanwhile, you cannot effectively dive until your team is quite leveled, by which point Sona and her team will have starved you of kills and XP (by killing you) while they get uncontested kills and heal back to max HP for free. Had a close trade and got the enemy to 10% HP but they won and you died? Typically, on ARAM, that's ok as then your team can finish the low HP enemy off. Sona? lol nope just let them sit back for a minute or 2 and they are once again full HP.
You may say "But warmog's offers this possibility". Yes, but warmog's requires 3000+ HP in order to activate, which will require 1 full HP item purchased before the completed warmog's. Consequently it can only be built on full tanks or on bruisers as a later item. Point is , Warmog's only becomes a possibility quite far into an ARAM match, whereas Sona basically provides a Warmog's for each of her teammates from the start of the game, 0:00.
You may also say, "Soraka is just as bad!". Again, you would be mistaken. Soraka wastes her own HP to heal her teammates, leaving herself actually vulnerable. And, in order to continue the healing, Soraka actually has to put herself at risk by getting in range to land her Q. Yes, Soraka can build a Warmog's (which is in fact quite OP), yet see above and realize she won't be able to do that until 15 min+ into the match.
Sona can be beaten, but you need a hard engage/ burst comp. If you do not burst 3+ members of the enemy team in a 5v5 in less than 4 seconds or so, Sona always wins. Her and her team can run away and hide under turret, and just wait til they are full health (while you are still low from the fight), and then put back on the aggression and win through sheer HP.
Champions are disabled on URF and other featured game modes because they in fact are extremely OP and break the mode due to alternate scenarios which diverge from the aspects of Summoner's Rift which champions are balanced around. Why can't we be consistent and remove Sona from ARAM? She is overly strong on Howling Abyss due to the nature of the map; at the very least, she needs an actual nerf. No, that -50% healing nerf was not sufficient. That is how broken this champion is on this map.

leaving her unhampered by mana and then places 2 points in her W.
