Just kinda thinking out loud here...
An idea for the INT fighter could be a series of 'probing attacks' to gauge the strength and ability of your opponent. On a successful attack, forgo doing damage in exchange for information about the opponent (HP, Saving Throw modifiers, or the like).
Alternately, the 'probing attack' could be used to increase your damage on the next successful hit. This could be achieved by a flat modifier (boring), rolling the damage more than once and taking the higher number, or automatically giving max damage.
I'm a little wary of "don't do anything now to do something later". Probing with your attack to get information = good. Giving up the damage you'd do = not so much. Especially as most 5e combats aren't that long that most of the time it's better just to try to inflict "condition: Dead" on the opponent.
The "no damage now for double later" is "you'll have two attacks worth of damage total. do ti normal and it's half now. Do it special and it's none now. Huh?". So it would need to be bigger than that. But even there, I'm reminded of playing Earthdawn where casters needed to spend actions to get "threads" to power their spells, so you had these null actions often. When you might only have an action every 10-15 minutes (depending on party size and how many foes the DM is running) I'm leary of that - it doesn't feel like you're contributing even if you will be.
So something like:
Probing Attack: Once per round on a successful hit, you learn one thing about your opponent: Max HPs, total damage taken, best save, worst save, movement speed and modes, all resistances/immunities, or any vulnerabilities. If you are proficient in Investigation you may pick two.
(Once per round is to keep the RL speed up since it's a separate DM interaction.)
Anticipate foe: When you take the Attack action, you have advantage on all weapon attacks, natural attacks and ability checks for special attacks like grappling until the beginning of your next turn as long as you damaged the target with a weapon attack since the beginning of your last turn.
You may do this a number of times equal to your INT or WIS modifier (min 1). Uses are restored on a long rest.
(Using the Samurai as a guide that at-will advantage on all attacks shouldn't be too often per day. Also note that it's "since the beginning of last turn" so reaction attacks count for damaging, and "until the beginning of your next turn" so you get the bonus on reaction attacks as well. Plus it counts for shoves and grappling.)