This community seems distrustful of, uhm, aliens. It can be seen the forum's statistics: there are two distinct groups of users, those who come here for quite short time and never come back, and everyone else. The latter eventually become hero and legendary users, and the former remain foreigners forever.
Is there any way for newbies to build reputation besides spending months to become a regular? Maybe some kind of a guarantee given by an already reputable user?
Reputation is something that takes a long time to build and is lost very quickly. Therefore, there is no "magic" way to "gain" a reputation quickly. You will have to wait months, but if you have the skills, knowledge and just have something useful to say, then on the forum, this can speed up the process of gaining a reputation. There were such examples when new users grew very quickly in the eyes of forum members, but these people already had an impressive background in real life.
Therefore, stop reflecting and start sharing something useful with the
BTC-community.