checks (with the assumption that cap9 is max attack cb/guts. only moves assumed from cap 9 are dark and ground. some checks may not be or fare well in ou but may come into play if cap9 over centralizes)
leafeon - even with min atk (neutral nature, max hp/def) leafeon leaf blade can do upwards to 75% cap9. while it only takes about 41-49% from a crunch. with only burn/poison and leftovers in play this should be more than enough for leafeon to handle. with good ev spreads and leafeons 95 speed it can at least speed tie, although sucker punch becomes an issue.
abomasnow - can ohko with min atk life orb ice shard and hail. needs defensive investments. sucker punch can become an issue if it switches on on a crunch. aboma is a team liability.
toxicroak - fairly obvious what will happen. needs choice scarf to outspeed upon a switch in to threaten.
counter
hippowdon - bulky version with slack off counter fairly well, healing back just over as much as the average attack it will be hit with (earthquake). with burn/poison in play, cap9 wont want to stay in for long and hippow can throw back an earthquake at around 30%.
honchkrow - resists dark and immune to ground lets it become a good switch in. min hp def honch takes about 47-55% from crunch so some investments to defence would be wise. even without honchkrow has superpower.
cacturne - cacturne resists both of cap 9s stabs, min defs take 70-82% from earthquake, 56-66% from crunch. can ohko back with seed bomb or near ohko and steal back a lot of health with drain punch. more defensive spread with choice scarf would be best.
shiftty -like cacturne, with better hp and worse atks. 61-72% from earth quake, 49-58% from crunch. can still threaten cap9 with s/e grass moves.
note: been up for a while, numbers starting to fuse together, calcs should be taken for rough estimations.
Which is something I've been meaning to bring up. Why is every iteration of CaP9 in the Counters Thread the Guts Sweeper? I don't think it would be terribly difficult to assume that "predict a resisted attack (or give it death fodder to get a free switch), switch in something faster than it, then attack with neutral-or-better attacks" strategy would absolutely destroy it.
its best to envision this within the worst case scenario, and guts sweeper will probably be used often. all of the pokemon posted in this thread all have a better chance to become counters iinstead of checks if cap9 is a of a bulkier version.