Most knowledge of Gothic is derived from fragments of a translation of the Bible made by the 4th-century Gothic bishop Ulfilas (or Wulfila). The largest and most splendid of these fragments is the Codex Argenteus, containing about half of the Gospels. The Gothic alphabet, traditionally devised by Ulfilas, consisted of 27 characters: 25 modified Greek symbols and 2 runes.
Here are some main traits distinguishing Gothic from other Germanic tongues:
1) We know that Common Germanic had three voices: active, passive and
medium, but only Gothic preserved all three, using mediopassive voice in
the present and past tenses.
2) Gothic used the method of reduplication (double stem) in constructing the perfect stem of the verb. This feature is common with Latin and Greek, but is not seen anywhere else in Germanic.
3) Diphthongs were shorted into long vowels in Gothic, and ai > é, au > ó.
4) The strong verbs of the V class lost the suffix -j- (ligjan > ligan)
Gothic was extensively rich with preverbs, or verbal prefixes, which
were quite productive in making new verbs. Gothic died leaving just a small
dialectal group of Crimean Gothic which can hardly be considered as a descendant
of this tongue.