THE SECRET OF CASINO DELFINO
Arguably the easier of the two Sirena secrets, the casino sectret also uses an even more beneficial skip than Sirena 3 going straight over the heavy RNG slot machine segment. Although the harder first cycle version of this level can be hard to learn, it becomes easy very fast.
Sirena Entry Movement
As every level in Sirena Beach involves talking to the Hotel Manager, they all have the same beginning movement. The most efficient is to do a dive rollout in the Up Right direction, and to do a single jump, while spraying, towards the stairs and dive into the water. It can be tricky at first, but only changes based on the length of the rollout
Casino Skip is very useful in all categories, allowing you to skip very heavy RNG segments with the slot machines. It is done by clipping through the wall above the curtain leading to the pipe. In order to grab the invisible ledge do a sideflip on the wall of the fountain (see example) and do a spin wall kick. After this you should have enough height to hover and grab the ledge. Climb up and immediately walk to the right (looking from the casino entrance). Since this ledge is buggy you shouldn't fall off even if you walk forward at full speed. After changing Mario's direction, sidestep for a short amount of time toward the curtain, then do a single jump and dive in mid-air.
Getting Around the First Cube
If you are trying to learn the faster Sirena 4 strategy of getting straight onto the cube moving across the gap there are a couple ways to do it. I do this strat a bit differently than most, but I'll give both. The first is to simply walk around the cube at the beginning on its left and dive rollout into a spinjump dive. The second and slightly more complicated strat I use is to dive rollout onto the top left corner of the yellow square in the ground and then dive rollout into a spinjump dive. The first strat is much easier to learn, however the second has a solid visual cue although to my knowledge I am the only one who does this.
Momentum Spin on the Big Cube
I wouldn't recommend trying this unless you are very confident in your unbuffered spinjumps, but there is a tricky momentum spin you can do on the final cube to get to the shine faster. This is one of the harder momentum spins in the run since it isn't done through a dive. First, dive rollout on the steep surface of the turning cube and once you get closer to the shine platform, run in a tight circle and jump with the control stick pointing towards the shine. While running, the momentum will be cancelled if you run too tightly and get the sideflip dust animation.