There we go... the timestretching feature of VI Pro is cool, but also frightening (at least for me): you can do so much with it. You can finetune the sound of the articulation just by drawing a time-curve (for example you want the vibrato to be earlier but the transition should stay as it is; or you want faster transitions but the sustain should not be altered; make tremolos faster / slower). And you can define different curves, so you can use the unaltered with the modified/multiple modified articulations together. (now I feel the urge to experiment what a tremolo that starts slow and gets faster would sound like...)Well that's VSL - Here the official List:
And with VIro you can create additional variations of these articulations (longer, shorter, ...)
The default vibrato is not what you want? Use the humanize function and draw your own vibrato in it (or use a preset).
And these are only two functionalities that allow you to tweak the sound. If you go full crazy you can combine these and also modify attack, release, transitions and more.