using System;

using System.Linq;

​

var buffs = new Buff[]

{

    new BuffA { Target = 0, Type = 0, Value = 30 },

    new BuffA { Target = 0, Type = 0, Value = 60 },

    new BuffA { Target = 0, Type = 1, Value = 10 },

    new BuffA { Target = 1, Type = 0, Value = 80 },

    new BuffB { Value = 30 },

    new BuffB { Value = 60 },

    new BuffC { Value = 10 },

    new BuffC { Value = 20 },

};

​

var group = buffs

    .GroupBy(x => x.GetMergeType(), x => (name: x.GetType().Name, value: x.GetValue()))

    .Select(x => (x.First().name, x.Sum(y => y.value)))

    ;

group.Dump();

​

public class Buff

{   

    public virtual int GetMergeType()

        => GetType().GetHashCode();

    public virtual int GetValue() => 0;

}

​

public class BuffA : Buff

{

    public int Target { get; set; }

    public int Type { get; set; }

    public int Value { get; set; }

    public override int GetMergeType()

        => (base.GetMergeType() * 6151) ^ (Target * 3079) ^ Type.GetHashCode();

    public override int GetValue() => Value;

}

​

public class BuffB : Buff

{

    public int Value { get; set; }

    public override int GetMergeType()

        => GetHashCode();

    public override int GetValue() => Value;

}

​

public class BuffC : Buff

{

    public int Value { get; set; }

​

    public override int GetValue() => Value;

}