While CSS passage transitions give you a good degree of creativity with regards to transition animations, a good many potential effects require Javascript. One such effect is the oft vaunted "typewriter" transition:

(function(){postrender.typewriter = function (b) {
if(this.tags){var r=new RegExp("t8n.typewriter.([0-9]+)(?:[^0-9]|$)","g");var t=r.exec(this.tags.toString());
if(t){typeout(b,t[1]+0);}}return b;};var typeout=function(c,t){var Furl=function(current){this.n=current;
this.out=false;this.data=current.nodeValue;current.nodeValue="";this.kids=[];var cn=current.childNodes;
if(current.style && current.style.display=="none"){return;}while(cn.length>0){var f=new Furl(cn[0]);
current.removeChild(cn[0]);f.out=true;this.kids.push(f);}};var nodes=new Furl(c);
var unfurl=function(furled,d){var n=furled.n;if(furled.out){d.appendChild(n);furled.out=false;
}if(furled.data){n.nodeValue+=furled.data[0];furled.data=furled.data.slice(1);return true;
}for(var j=0;j<furled.kids.length;j++){var ret=unfurl(furled.kids[j],n);if(ret){return true;
}}return false;};var title=state.history[0].passage.title;var intr=setInterval(function(){if(state.history[0].passage.title==title&&unfurl(nodes,null)){return;
}clearInterval(intr);},t);};}());

To use it for a passage, tag the passage with "t8n-typewriter-" followed by the number of milliseconds between each character appearing - for instance "t8n-typewriter-10" or "t8n-typewriter-2". If you have a lot of text, a low number is highly recommended.

("t8n" is a numeronym for the word "transition". For this and any future transitions of mine, "t8n" will denote a tag that invokes that transition.)

This can be combined with CSS transitions! See this example to see a combination of the two.

Caveats:

1. Images amid the text will currently appear instantly, as if they were single characters. This may appear a little jarring if they are below text.
2. This transition currently does not apply to the <<replace>> macro - replaced text will simply appear normally.
3. This transition currently may interfere with the timing of the <<timedreplace>> macro. If the <<timedreplace>> macro triggers before it has been fully typed out, then it will not function correctly. Simply make sure that the <<timedreplace>> is timed to trigger only after it appears.

These caveats may be improved in future versions. Other possible improvements may include a macro designed to alter typing speed within the text itself, so that the full range of pauses, staccato, blurt-outs, etc. as seen in various RPGs, can be replicated in Twine.

Version history:

1. 22-3-13: Initial.