at least 4 or 5 skills including front walk-over and multiple back-walk-overs will score the highest. If you can do a back extension roll, that would be the hardest most "creative" level 1 skill I can think of to throw in to a pass.
And coaches don't necessarily assign tumbling passes. When I coached level 1 two years ago, I told the kids that they had to do at least 4 skills and they could choose their tumbling pass. I, of course, got final say but they were all smart enough and tried to out do each other by adding in a bunch of variety of skills. You'd be surprised at how creative even the younger kids can get when it comes to choreography.