Gragas (2G) - Brawler

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Gragas is a brawler who has the ability Chemical Rage. He heals a percent of his health (Health & AP) over a duration of seconds. Then, he deals (AP) magic damage to adjacent enemies and chills them.
Gragas is a tank, but in the past healing for a percent of health tends to be a lot stronger in the early game than it is in the late game. So, he will likely fall off hard as the game continues, but be a solid early game pick up.
Pyke (2G) - Voyager

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Pyke is a Voyager which gives damage amplification and shields to himself. His ability Marked for Death makes him reposition up to one hex to throw a harpoon at the furthest enemy.
The harpoon pulls the first enemy hit one hex forward and deals (AP) physical damage. Pyke then teleports behind them and cleaves, dealing (AD) physical damage to them and (AD) physical damage to nearby enemies.
Viktor (3G) - Channeler

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VIktor is a 3 cost unit with the ability Psionic Storm. Viktor channels a one-hex psionic storm that follows enemies. Each second, the storm grows larger and deals (AP) magic damage to enemies within, reduced by a percent for each hex from the epicenter.
This is damage over time, so Viktor will not always be the best at cleaning up units. This means that he will likely want another carry with him or to be well itemized to actually be able to complete kills.
Master Yi (4G) - Marauder

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Master Yi has the ability of Psi Strikes. With his passive, every third attack strikes an additional time for passive (AD) bonus physical damage. For his active ability, he briefly meditates, entering a Psi-State for a number of seconds, gaining omnivamp, attack speed, and increased movement speed.
Twice a second, he fires a psychic projection at a random nearby enemy that deals (AD& AP) physical damage.
Sona (5G) - Commander + Shepherd

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Sona has a 5 cost unit with the ability Psionic Crush where she hurls a chunk of magnetic debris at the nearest target without one, dealing (AP) magic damage and sticking it to them. If an enemy with debris dies, it passes it to the nearest enemy without one.
Every number of casts, instead rip off all debris dealing (AP) magic damage, then crush all the debris onto the target, dealing (AP) magic damage and briefly stunning them.