Flanking allows both your character when working with your allies, as well as groups of your enemies, a simple way to gain advantage when making attack rolls against a common foe.
A creature can't flank an enemy that it can't see. A creature also can't flank while it is incapacitated. A Large or larger creature is flanking as long as at least one square or hex of its space qualifies for flanking.
When a creature and at least one of its allies are adjacent to an enemy and on opposite sides or corners of the enemy's space, they flank that enemy, and each of them has advantage on melee attack rolls against that enemy.
DMG p251
Even the most skilled and powerful of warriors is unable to defend themselves when faced with too many enemies working together.
When a character of medium size or smaller has four or more allied and intelligent enemies adjacent to them, or able to attack them with melee weapons, they suffer a (-5) penalty to their armour class. If instead, they are completely surrounded, by eight enemies or more, they suffer a (-10) penalty to their armour class instead.
When choosing to roll for hit points during character advancement a player may re-roll ones when rolling for those hit-points.
A character can drink a potion, themselves, as a bonus action. It remains a full action to feed a potion to another creature.
Using Bardic Inspiration as an example; many abilities, features, feats, etc. have the following or similar verbiage:
The creature can wait until after it rolls The D20 before deciding to use the Bardic Inspiration die, but must decide before the DM says whether the roll succeeds or fails.
In any and all of these cases, this game will allow more leeway to the timing of such abilities, it will be possible to use these abilities after the result of a role has been declared by the GM, within reason.
Drop the ‘normal’ inspiration rules, players get a “charge” of inspiration at the beginning of each session. Still a binary on / off mechanic.
During combat, for a player to be able to "see through" an illusion, cast by another player, they must roll their Insight against the casting players spell-save DC.
If the illusion is one used often then players may roll Insight with Advantage.