Running following OS; 

Linux  3.16.0-4-amd64 #1 SMP Debian 3.16.51-3 (2017-12-13) x86_64 GNU/Linux

Getting this following error when trying to run;

./MewnBase: /usr/lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by ./MewnBase)

Shows 3.4.21 is not installed;

/home/user/Documents/mewnbase-linux# strings /usr/lib/x86_64-linux-gnu/libstdc++.so.6 | grep GLIBCXX

GLIBCXX_3.4
GLIBCXX_3.4.1
GLIBCXX_3.4.2
GLIBCXX_3.4.3
GLIBCXX_3.4.4
GLIBCXX_3.4.5
GLIBCXX_3.4.6
GLIBCXX_3.4.7
GLIBCXX_3.4.8
GLIBCXX_3.4.9
GLIBCXX_3.4.10
GLIBCXX_3.4.11
GLIBCXX_3.4.12
GLIBCXX_3.4.13
GLIBCXX_3.4.14
GLIBCXX_3.4.15
GLIBCXX_3.4.16
GLIBCXX_3.4.17
GLIBCXX_3.4.18
GLIBCXX_3.4.19
GLIBCXX_3.4.20
GLIBCXX_DEBUG_MESSAGE_LENGTH

Does anyone know how to update GLIBCXX or fix this issue?

Thanks!

First time I've seen an error like that, will try and look into it more.   In the meantime, as a long shot... have you tried the plain java version?  (assuming you'd have OpenJDK or Java installed on your machine).

I followed parts of some steps from similar question asked on another site, changed /etc/apt/sources.conf to stretch instead of jessie, then ran apt-get dist-upgrade, the game now runs. No sound, but will have to keep digging to see what's causing that.