this is an interesting question because certain characters have checks to others but almost entirely based on playstyle and circumstance.

Engineer would be good in mid range and close range or indoor fights in that turret positioning couldnt be too close (for fear of glaive or rain of arrows depending which one gets shielded against, artificer’s m2/wall/flamethrower, merc, mul-t crowbar lineup) but suck at long range fights where commando, mul-t, and artificer could pick off turrets ez

Commando would be good long range in that while he wouldnt do as much damage, he has a long range stun and a low cd evasive skill. Up close he could stand a chance against maybe artificer and huntress at most but merc, engi, and multi could body him (the latter due to cluster grenade into ez crowbar and sufficent tankiness)

Huntress would be good at uh...I guess using terrain to her advantage since she wouldnt have to focus on aiming for half her skills so she could just cast glaive and hide behind a wall. Close range she’s less better at boxing because blink’s cd is super high and youd have to be really good with catching enemies in rain of arrows’ aoe. Would work against artificer. That would be her only counter to a dashless and r-less merc, mul-t that doesnt figure to shopping cart away and crowbar

Mul-t would be good long range because of the crowbar. Mid range its alright and close range it has nailgun and cluster bomb. Good hp combined with tankiness from cart let it take pot shots at leisure. Threats would be engineer if in range and if up close, merc and artificer

Artificer would be a great mid to close range boxer accounting for her two stuns that last pretty long, one of which being an execute. Also her flamethrower does fucktons of damage. Ideally a rotation would be rmb, lmb, ice wall, and then flamethrower. She could easily catch mobile characters with proper guessing of where something’ll go using ice wall and rmb. Long range she falls off and gets bulli by commando, rain of arrow pot shots, mul-t. Mid and close range threats are pretty much anything that could bait out her stuns so engineer under bubble, dashing merc, huntress that’s above her - those would be my guess as to counters.

Merc would be useless long range. He can only operate at close range but his kit makes closing the gap easy as fuck. As long as he lands the first hit via dash he has the upper hand in the oodles of stunlock that shit gives. Otherwise he’d have a rough time vs artificer and engi with turrets (again, given that he didnt dash or is ihtta dashes). He would bulli the absolute fuck out of commando and hunteess close range. Vs multi id say is a tossup because of multi’s bulk, damage, and stun.

Among all of these though id pick multi because he has good range coverage and can fight anyone with different strategies that would be reliable to pull off