2nd PC Patterns
A 4-height perfect clear requires 10 minos. Therefore, after an opening 4-height perfect clear, you will have 4 minos left from the second bag since each bag contains 7 minos. It turns out that you can arrange these 4 minos to give you a high chance of repeating a perfect clear.
One assumption that the guide makes is that the player will do his or her first PC with either the Perfect Clear Opener or Grace System, as these are widely used patterns for the 1st PC in real matches with a good PC chance (80%). There are only certain combinations of minos that are possible to be left after doing PCs this way, and they can mainly be arranged into ① patterns that have a T and ② patterns without a T.
While these are very practical patterns that are easy to solve, many of these patterns leave an extra S or Z. This is actually great for DPC, but it becomes a problem when you're attempting consecutive PCs. Look at this Google Doc created by Marfung37 for patterns that can help you save O or T for your 3rd PC.
Generally speaking, you will have a higher chance of PC if you have T left in your 4 pieces due to parity reasons.
TIOS / TIOZ and OTSZ will only appear if you PC with Grace System. They are covered with pattern 5.
OTLJ will not appear after either PCO or Grace System and therefore a corresponding pattern isn't needed. However, if you do your first PC a different way and are left with this, you can use this pattern shown below. ITLJ and TLJS / TLJZ won't appear either after PCO or Grace System, but there are patterns that work for them.
Patterns marked with only work for specific orders of those minos.
Note: TIOL / TIOJ has a optional separate pattern that has a 100% PC chance.
This pattern covers TIOS / TIOZ and OTSZ which will only appear if you PC with Grace System.
Redundant solution with a potential extra TSD:
The third and tenth solution will potentially give you an extra T-Spin.
Redundant solutions with potential extra TSDs:
These are some other patterns that you could use that were not covered in knewjade's guide.
There are 10 solutions. You can use this if you'd like a higher chance with OJSZ since, while easy to solve, Pattern 2 will only give you an 80% chance.
Pattern 2 covers TIOL, but there is actually a 100% pattern that you can use when you get it. Learning this pattern is optional.
You'll have a 100% chance of doing a PC with just 2 solutions, but these will always leave you with either an extra S or an extra Z, which isn't exactly the best situation to be in for your 3rd perfect clear. However, you'll have around a 63% chance to avoid that with these solutions.
If you did a perfect clear with an opener like MKO, there's a chance that you would have held the T from your first bag and be left with either TTSZ or TTIS. There are 35 solutions, but a lot of them can be considered repeats.
thanks stickmancomic for the tip on ILOZ for Without T - Pattern 2. thanks Kibble for the tip on Tetris and TSD solutions for With T - Pattern 5