The building blocks of English

Affixes

-tastic

Something outstanding, superb, or excellent.

The ending of fantastic.

This is a relatively recent colloquial formation, whose survival is as yet in doubt. The earliest example, still the most common, is poptastic, something superlative in pop music; others that have been formed on the same model (but which are much less common) include cybertastic, sextastic, and babetastic.