Sorry, I'll put the next Feats all in one post as they are all based on the same idea: trying to emulate 4e ''multiclass'' feats. I also want to add feats that allow the players to expand Inspiration to gain special feature other than just granting Advantage.
Wrathbearer
Prereq. 13 Str, any class other than barbarian
+1 Con or Str
Once per rest you can spend Inspiration to enter a fury-like trance for 1 minute. When the character enter this state, he gains 2x Con mod THP and gain +2 to damage roll with melee weapons for the duration of the effect.
Arcane Dilettante
Prereq 13+ Cha, any class other than bard.
+1 Cha or Int
- You count as a wizard for the purpose of item atunement and the use of spell scrolls.
- Once per long rest you can spend Inspiration to use your Action to cast a spell known by you or an ally within 15'. The spell cant be higher than level 2. Charisma is the spellcasting stat for this spell.
Divine Envoy
Prereq. Wis 13+, any class other than Cleric
- +1 Wis or Int
- Once per long rest you can spend Inspiration to enter a state of divine investiture. For 1 minute, you can replace any Charisma roll you make by a 10 after the original roll. For the duration you can speak and understand any languages.
Old Faith Initiate
Prereq. Wis 13+, any class other than Druid
- +1 Wis or Con
- You can understand the language of animals
- Once per long rest, you can spend Inspiration to take the shape of a small CR 0 animal for up to 1 hour.
Warrior Surge
Prereq. 13+ Str, any class other than Fighter
- +1 Str or Dex
- Gain proficiency in a martial weapon of your choice.
- Once per rest, when you spend Inspiration, you can also spend an Hit Dice to recover the same amount of HP or to make a saving throw against an ongoing effect.
Ascetic Training
Prereq. 13+ Wis, any class other than Monk
-+1 Con or Dex
- Damage with simple weapons 1d6 damage instead of their regular damage if lower.
- You have resistance to non-magic piercing damage as long a you wear no armor. On a turn you spend Inspiration, you can use the Dodge action as a Bonus Action.
Faith Militant
Prereq. Cha 13+, any class other than Paladin
- +1 Str or Cha
- Gain proficiency in a martial weapon of you choice
- When you use Inspiration on an attack roll against an Undead or Fiend creature, if the attack hits, you can add your Cha mod to damage. Choose Radiant or Necrotic for the damage of this attack.
Strider
Prereq. 13+ Con, any class other than Ranger
- +1 Con or Dex
- You have Advantage to resist any effect to would restrain, hold or slow you.
- You can spend Inspiration to ignore the effect of the two first level of Exhaustion for 1 hour.
Scoundrel
Prereq. Dex 13+, any class other than Rogue
- +1 Dex or Int
- You proficiency in Sleight of Hands
- At the start of an encounter, you can spend Inspiration to be automatically Hidden from all creatures in the encounter.
Mystic Birthright
Prereq. Cha 13+, any class other than Sorcerer
- +1 Cha or Con
- You gain the Thaumaturgy cantrip.
- Once per long rest, you can spend Inspiration to reveal your mighty lineage to your adversaries as a Bonus Action. Any non-allied creature with more than 5 Int within 30' must make a Wis saving throw against a DC of 8+prof+Cha or be frightened or charmed for 1 minute. The creatures can attempt the saving throw at the start of their turn.
Occultist
Prereq. Int 13+, any class other than Warlock
- +1 Int or Cha
- You gain proficiency in Arcana
- Once per long rest, you can invoke your power of foresight by spending Inspiration. When this happens, the DM should give you a relevant piece of information regarding important events likely to occur during your current adventure. You may gain clear images of where you should go, places to be wary of, a wanderer you can trust and so forth.
Loremaster
Prereq. 13+ Int, any class other than Wizard
- +1 Int or Wis
- Gain the Prestidigitation and Mage hand cantrips.
- Once per long rest you can spend Inspiration to gain proficiency in a Skill, Tool or Language you're not already proficient with for 10 minute. For the duration of this effect, you use Int instead of the regular ability for the use of the skill.