2nd PC Patterns
A 4-height perfect clear requires 10 minos. Therefore, after doing 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 in a way that will 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 a certain combination 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.
Don't be intimidated by the number of shapes shown on this page. A lot of them are just variations of these basic shapes, which you might already be familiar with:
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 certain orders of those minos.
The only pattern for TLSZ / TJSZ.
Note: TIOL / TIOJ has a optional separate pattern that has a 100% PC chance.
The only pattern for OTLS / OTJZ.
This is the only pattern that covers ITSZ.
This pattern covers TIOS / TIOZ and OTSZ which will only appear if you PC with Grace System.
Pattern 2 covers TIOL, but there is actually a 100% pattern that you can use when you get it. Learning this pattern is optional.
These are some other patterns that weren't covered in knewjade's guide that you could use.
You will always be left with either an extra S or an extra Z if you use this, which isn't exactly the best situation to be in for your 3rd perfect clear.