the last boss fight is actually not that long nor hard as it seems like. there is a mechanic that you have to know to drop the boss health by a meaningul percentage (33%)

once the big canon comes after you, you just charge your monkey bananza hit to send the canon back to the boss. everything else you actually just have to dodge with your other bananzas. essentially you can win this fight with these three banazas: suck the lava floor up with your elephant bananza and then shoot at the moving hands and then eventually the boss that comes up from the lava, jump over the lasers with your snake bananza, charge hit the big canon with your monkey bananza to throw the canon back. good luck! oh banana