**5x5x4 Cuboid**is a fully functional and proportional cuboid. It's mass-produced and is a really enjoyable solve. You can buy it here.

**The Basic Plot**

- Solve centers.
- Solve inner corners
- Reduce edge triplets.
- Solve reduced 3x3x2.

**Step 1: Solve Centers**

We begin by placing the white and yellow centers. It's fairly easy and done a we would a 5x5x5 cube. To place the last few, we use the corner piece series for cuboids: (U r2 U' l2) x 2.

Next, we bring together middle layer pieces which match, then move them off onto an adjacent face using the edge piece series.

We can now complete the inner cage by solving what are essentially the "corners" of the inner 5x5x2. This involves a corner piece series which is similar, but not the same, to the previous one: (u R2 u' L2) x 2.

Instead of turning all outer layers, this series will turn the inner layer for upper turns, but the outer layers for left and right face turns. It cycles the pieces LBu->FLd->FRd. And of course, its mirror can also be used.

Next, we bring together middle layer pieces which match, then move them off onto an adjacent face using the edge piece series.

At the end, we will either have three edges remaining to be joined, or else two. If it's two, the fix is to turn the inner slice 180° such that it breaks the yellow/white centers. Once this is done, we re-solve the yellow/white centers using an even number of turns, and then continue solving the middle layer centers. At the end, we will be down to three remaining, which can easily be dealt with.

Once all middle layer pieces are in completed triplets, we place them simply using edge piece series.

**Step 2: Solve Corners of Inner 5x5x2**Instead of turning all outer layers, this series will turn the inner layer for upper turns, but the outer layers for left and right face turns. It cycles the pieces LBu->FLd->FRd. And of course, its mirror can also be used.

If you find you need to swap two "corners", apply the same fix as for a 3x3x2. Turn the two bottom faces 90° and then re-solve the centers, followed by the remaining corners. In doing this, you will fix the problem of needing to swap two corners.

**Step 3: Reduce Edge Triplets**
This is done in much the same way as you would on a 5x5x5 cube. Bring together edge pieces to make a triplet, then use an edge piece series to move the completed edge triplet onto a different face. Then return the centers.

Often, you'll get down to the final two edge triplets to make and find that it's impossible to complete them using the same routine as above. In this case, you'll need to apply a fix, to enable you to complete them. Here's how it's done:

- Hold the puzzle with the 5x5x5 sides at left and right
- Turn the bottom two faces 180° and then resolve the centers and inner corners
- Re-solve the edge triplets

**Step 4: Solve Reduced 3x3x2**

At this stage, the only types of pieces left to solve are the outer corners. This is because the inner cage is completely solved, and all the edge triplets have been placed.

Once again, we use a corner piece series, but this time we turn only the outer layers: (U R2 U' L2) x 2.

If you need to swap two outer corners, apply the following fix.

- Turn a 5x5x5 face 90°
- Re-solve the edge triplets
- Re-solve the 5x5x2 cage
- Re-solve the outer corners

And that's it. Your Ayi's 5x5x4 is now solved. I trust this site has been helpful. If you have any questions or want some clarifications, please use the comments to do so. You can buy it here.

I am solving this now, following carefully your tips in EACH video ! :)

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