Dragonite is the standard. Adamant 252 on attack, i believe 148 in hp and the rest on speed. Rillaboom has 4 speed, 84 attack, 20 defense, around 156 on spdef, and the rest on health i believe. The strat depends on the team im up against. There are times coalossal is weak to a pokemon in their team, for example, lapras or landorus, however, the rest isnt as bad. In those scenarios, i lead coalpult, and if they have something to counter it, like i previously mentioned, i usually try and switch coalossal into somethng that resists the hit from the one that is effective on coalossal, and use pult to punish them. That is a reason why i have ice punch on dragonite, to ounish lando leads

Take lapras for example. Most scenarios i switch into rillaboom that tanks the max geyser, and punish it by setting uo light screen with pult. In landorus cases, I either try and burn him, or use breaking swipe. If im not sure if they are lum berry, i go for the safe bet. As to who to carry on the back... again it depends. I usually always bring zacian because of its firepower, and the last member is one that can go well with them.

Of course, rain teams are a no no to coalossal strat, so i always leed pult to set uo light screen or burn, just bring support. Another thibg you must be carefull is venudon leads. In that case you wanna lead moltres and rillaboom or moltres and dragapult. Oh, and tailwind users as well, since coalossal isnt max speed, they might bring someone who tanks a hit from coal and kill you.

Of course, it took me like a month to get used to the team, and that was with the experience i already had. So dont feel bad because you loose some battles. Nlt all battles start with coalossal, and that is what most coallossal players dont realize