Blend type in Illustrator in seconds, Create some type on the art board. Create some more words somewhere else on the art board. Doesn't have to be the same words or letters. Of course, if you have some letters already then you don't need to create any more
You could also just duplicate some words by selecting some letters and holding down the alt / option key and dragging to duplicate. You can change the font, change the size, scale, rotate it, change the color of the those characters and much more. Select and then click the first object and then click the other object and you will see an instant combo with the current option (probably the smooth color default)
The options include spacing (smooth color, specified steps and specified distance) as well as orientation. It is a live effect and can be changed at any time for the current selected object. Press return and change the setting such as changing to steps and setting a particular number of steps. Sadly, there is no scattering option so you can add some jitter to the object
Use the direct selection to just select the words you want to change. Say you suddenly think it would be a nicer combo of black to green than black to red, select the red words with the direct selection tool and then change the color and the object will change to reflect that color change. You can also add in rotations or scaling etc for the individual text (though avoid the reflect tool as that ends up with some truly dire text unless that is what you want). You can also change the words in the objects but the results are variable, sometimes the colors work well but there is some serious distortion. Or use a different font with the object as well as lowering the opacity of the right side words.
If you select the object, you can see a spine / path running all the way through it. You can edit this path. Double click it and enter isolation mode. You can re-size / reduce the spine. Add points to it and move those points etc (use the add anchor points or the curvature etc) You can then move those points to create a jumble of text.
If you use the curvature tool and add more points, you may like to change the specified distance or steps.
How to expand it ? Object menu and expand with the entire object selected
Up until you expand it, it is live and can be modified over and over. Object menu and ungroup (twice) to access the individual paths and tweak them or perhaps use the layers panel.
You can select any open path as the spine. Create your combo object between paths and then create a spiral or another design and then select both the objects and go to the object menu and blend and replace and suddenly your design will look very different. You may need to tweak the number of steps or the distance (and as it is still live), just go to it and double click the icon.
You can also apply most things via the commands in the object menu and blend such as make (and release) as well as replace and reverse and expand.
If you have two or more objects made up of lots of word combos, can you do the same with them ? Can't be done but you can always expand and then work with them. Select both objects and then go to the object menu and expand and then go back and it should now work, though sometimes very complex designs with multiple entries never ever end up looking great.
For most of this tutorial been talking about two objects but you can use multiple objects, perhaps 5 or 6 or more and click between them to create an interesting combination which can then be modified via the spine etc.
You don't have to use just filled characters, you can set the fill (two or more) to nil and just use a stroke and use it with those to create amazing stroke designs. You can then change the width etc. However, width profiles (sadly) fail to work with this feature
However, you can select a word combo object and then object menu and expand and then use that in a repeat, it is just not live any more and cannot be edited, though the repeat object is live and the instances etc can be changed as can the design itself by double clicking one of the instances.