Ever since I saw on the title screen to "kunio ice hockey"(I think you know which game i mean, I don't want to have to write the whole japanese title) that it had a 4P mode I've wondered, is that even possible? if so, how? Does there exist a multitap for famicom?
Yes, there's at least the 4-players adaptor (https://www.google.com/search?q=4%E4%BA%BA%E3%83%97%E3%83%AC%E3%82%A4%E3%83%A4%E3%83%BC%E3%82%BA%E3%82%A2%E3%83%80%E3%83%97%E3%82%BF&es_sm=93&source=lnms&tbm=isch&sa=X&ved=0CAcQ_AUoAWoVChMIr9K5gL3ExwIVAbMsCh3DrwoW&biw=1745&bih=903) from Hori.
(http://www.tomorege.com/img/contents2/fc_syuuhenkiki/etc_4player.jpg)
I love Hori. Then, as now, always useful.
I actually have one of these boxed. Nice unit with sturdy construction.
I always thought that a "four player adapter" was simply a pair of controllers joined together with a Y-type plug with the 15-pin connector. You already always had two on the console itself until the AV Famicom came around in 1993 or so.
There are various variants of multitaps for Famicom. Some external controllers has an expansion port on the controller so you can daisy-chain player 4 on it. Supposedly they all work the same electrically.