I said it before and I repeat it again: I like older formats for trying more ideas than modern ones. DMV was surprisingly full of unconventional approaches to video compression.
First of all, it uses fixed-size blocks with palette and image data occupying initial part of the block, and audio taking fixed size tail part of that block.
Then, there’s image compression itself: frame is split into 2×2 tiles that can be painted using 1-4 colours using pre-defined patterns, so only colours and pattern indices are transmitted. Those indices are further compressed with LZ77-like method that has only “emit literals” and “copy previous” (with source and destination allowed to overlap but with at least 4-byte gap for more efficient copying).
And even that is not all! I actually lied a bit because in reality it is 2x2x2 tiles since one pattern (using up to 8 colours) codes two 2×2 blocks in two consequent frames simultaneously. Now that’s an idea you don’t see every day. There are many codecs that code colours and patterns separately (like Smacker or System Shock video), some use a variation of LZ77 to compress data even further, but the only other codec I can name that coded two frames at once would be H.263+ with its PB-frames (and it was mostly interleaving data in order to avoid frame reordering, not sharing common coding data between frames).
Searching discmaster.textfiles.com for large unrecognised files returned more hits so I hope that some of the remaining formats will also feature some refreshingly crazy ideas. Now I only need time and mood for reverse engineering.