This is not the best card. But. There is a place for it.

Mano a Mano is primarily let down by its restriction of "First action only", this means that it cant be used by a dedicated fighter to tackle down enemies engaged with their dedicated cluehounds.

This card is good in decks that go out of their way to very literally "hunt" for enemies on their own. You use "Let me handle this!" and On the Hunt to ensure that enemies that might've spawned on your friends get spawned on you instead. The circumstance where Mano a Mano is good is when enemies spawn on you and you can start off a fight right in their faces and these combat support cards can make that happen manually.

The most efficient way to put this card to use is in decks for characters who benefit from the monsters they battle, William Yorick and Roland Banks come to mind. Zoey Samaras can also put this card to good use.

Other cards that synergize include: Guard Dog and Beat Cop for more auto-damage. Evidence! to then turn hunted enemies into clues. "I've had worse…" to fuel the warmachine through sustained battle. Every single weapon, obviously!

I find that use is a bit too conditional, but then again so are the new "composure" cards.

The 1 horror shield perk is not terrible but guardians have better ways to shield/prevent/heal horror. The 1 exp cost makes it inferior for this use.

A rich Zoey might benefit from it under certain cicumstances but it's a bit of a head scratcher for Mark and Roland who are not usually resource-plenty. But even with Zoey, and it likely won't survive too long in your play area for you to benefit from it consistently. Mark can use Sophie to buff himself far more reliably and without resource cost.

The fast trait and cheap cost are the evident advantages compared to Physical Training if you're hoping to buff your combat skill. No willpower option however, for which a buff is always handy.

Also, correct me if I'm wrong, assets can only be played during your turn, so you cannot surprise-buff your agility for an encounter card agility test (because when are you buffing your combat during Mythos anyhow?) That means you need to have it played beforehand, adding more to its chances of a premature break.

The slot in your deck is probably better spent on other cards. Likely you'll just commit it than spend two resources to play and trigger.

Use Oops! to deal damage against enemies with: High value; Retaliate; Aloof; or who are engaged with another player. Engage with and attack another enemy with a lower Fight value (the ideal would be a Fight of 2, since it would be impossible to fail the attack by more than 2), without Retaliate, or who are not Aloof.

Do so without bonuses of s / icons, preferably using an attack with a natural Damage bonus (i.e. not one that depends on the attack being successful), and better still not using your investigator's better skill-values. Thus favourable choices (when available for the investigator's deck) are: Backstab; .32 Colt and Shrivelling [also Knuckleduster though this will result in the initial 'phoney' target doing its own Retaliate damage to you].

Since damage dealt by Oops! is not the result of an attack on the "target", failure now results in damaging the higher Fight-value enemy/bypassing its' Retaliate/avoiding risks of injuring another player already engaged with it.

This can be a directed tactic or merely to hedge bets facing multiple enemies. It is more practical cooperating with fellow players; and when your deck and/or that of a team-mate includes cards apt for bringing weaker and stronger enemies together and/or engaged with the attacker (e.g. Shortcut; "Let me handle this!"; On the Hunt; Taunt; Heroic Rescue).

Not a review or anything, but having mentioned this via the GutHub link at the bottom of the page, which seems to have gone unnoticed, I'll mention this here in the hope of correcting an error.

The encounter set included in Carnevale of Horrors, is actually called 'Carnevale of Horrors', not Venice as listed here on arkhamdb.

This card actually says: You lose an action. Other investigator may take an additional action.

Well i don't know if this is good or bad card to include it to your deck. As a seeker in multiplayer you need every action to gather those clues so i'm kinda meh...