Mate Beggars are typically players- most likely young- who will walk up to practically anyone and beg them to be their mate. Hence the name "Mate Beggar". Not simply ask but more like spam their target with constant questions relatin' to the classic, "Will you be my mate?", "Why not?", "Be my mate!", "I'm going to report you if you don't be my mate!", etc. It's best to kindly turn these types of players down if ye' are to ever encounter one then block them. Although if they're goin' haywire and start threatenin' ye', it'd be best to take screenshots and report it to the staff team.
Insta-mates are simply players who will becomes mates with the first character they see and/or ask without gettin' to know who they're bondin' with. Insta-mates are a shorter term for "Instant Mates".
See if this helps in gettin' ye' successfully around the many maps of FeralHeart:
http://www.youtube.com/watch?v=2aPhakzpY-Y (http://www.youtube.com/watch?v=2aPhakzpY-Y)
Ye're very welcome, floofeh.