The following tweaks concern bards, fighters, sorcerers and warlocks.
Bard - Countercharm
At 6th level, you gain the ability to use musical notes or words of power to disrupt mind-influencing effects. As a bonus action, you can start a performance that lasts until the end of your next turn. During that time, you and any friendly creatures within 30 feet of you have advantage on saving throws against being frightened or charmed. A creature must be able to hear you to gain this benefit. The performance ends early if you are incapacitated or silenced or if you voluntarily end it (no action required).
Monkey Note: Since BA economy of the bard is already full with inspiration, moving this as a bonus action is fine, particularly when the power of it is so mild.
Fighter - Indomitable
Beginning at 9th level, when you make a saving throw, you can choose to succeed automatically. You must choose to do so before the roll and you can't use this feature again until you finish a long rest.
You can use this feature twice between long rests starting at 13th level and three times between long rests starting at 17th level.
Monkey Note: When the save DC is 22, if your Wisdom modifier is +1, you’ll never pass that save, no matter how many times you reroll. Fighters are supposed to be tanks/defenders, but have few defensives options. This is like half a legendary resistance. You need to announce it before hand, but it allows you to be that unstoppable force. Mind Control ? I don’t think so, you’ll still eat my blade.
Sorcerer - Metamagic
At 3rd level, you gain the ability to twist your spells to suit your needs. You gain two of the following Metamagic options of your choice. You gain another one at 5th, 10th, 13th and 17th level.
Additionally, when you gain a level in this class, you can choose one of the metamagic options you know and replace it with another option that you could learn.
Monkey Note: Sorcerer do not get enough metamagic options, they will always pick twin spell and quickened spell because they are the best ones, this doesn’t allow them any variety in gameplay. Allowing them to gain more of them over time allows player to create more unique characters.
Warlock - Agonizing Blasts
(Optional Feature, removes the Agonizing blast invocation)
At 3rd level you learn the eldritch blast cantrip, it doesn’t count against your maximum numbers of cantrips known. In addition you add your Charisma modifier to the damage it deals on a hit.
Monkey Note: Many new players fall into the trap of not picking either EB or Agonizing blast, which cripples their character. This is essential for the class to function, so it should not be optional. This boosts the warlock by giving them an extra invocation, but from experience, this is nothing gamebreaking, and helps the warlock along. In addition by locking agonising blast at level 3, it discourages multi classing (requires 1 more level).