a single brick is not that strong double01
too bad that accelgor doesn't have spikes in its moveset as that would give it more utility than just being hard-walled by the next pokemon we pick
because of this, i'm gonna pick dragontamer's escavalier. escavalier is a very difficult pokemon to wall and with return many of its counters, such as poliwrath, have a pretty tough time and are forced to recover early which can be used for a free switch-in. also the escavalier switches that are not 2hkoed by return (poliwrath, steelix etc) are all very passive pokemon and can be exploited rather easily. obviously aggron and his head smashes go against this theory though...
the other reason i am voting for escavalier is because it doesn't basically turn accelgor into a useless pokemon, like golbat and mr mime do. if you read the overused counter that pokemon warstory between doom and melee mewtwo, you'll notice how doom basically foddered four of his team members just to get in infernape / rotom-w and abuse them without them taking damage. in fact, a few of doom's pokemon were actually liabilities that could be set-up/spiked on and their absolute best utility was sacrificial fodder. i think it is important for us to ensure that every pokemon is somewhat useful in this rendition. while accelgor will never break through golbat and mr mime, it can chip at escavalier pretty well with focus blast, meaning that accelgor won't be entirely useless. i know the point of this exercise is to encourage finding the best possible counter for things, but rather than basically making it 6-5 by picking an incredibly specialised counter, we should try to pick something that gives the accelgor user some flexibility. escavalier is a good switch into accelgor but if the player plays well, accelgor could be a real nuisance. however by picking mr mime or golbat we are basically saying 'this pokemon is useless no matter how well you play' unless we partner accelgor with like scarf gothorita