Why the scale saved TTJ and the nails bits - the execution of the grand plan of Ji Ze

As the God Of Time Ji Ze is able to access his memories in both the past and the future (even foresee the future in Li Su Su's time, hence why the Mirror of the Past was created in the first place). So he devised a grand plan and executed it perfectly. The plan involved Li Su Su, the thread, the dream, the tear and its nails, the scale, and the tower scene (will not give spoilers to that scene, see it in episode 28th). The continuation of this plan we shall see in the immortal arc (again no spoilers to that here). His plan went as follow:

1. Created the Mirror of the Past in wait for Li Su Su. Also made sure to leave the immortals of the future with the words "the Devil God will only die if his bones are destroyed. If you kill his mortal form with the bones intact, it will make the Devil God appear." 

2. Trapped himself in the Barren Abyss for 10 000 years in wait for Li Su Su.

3. Told Ming Ye his plan after Sang Jiu was gone. Ming Ye created the Bo're dream and trapped himself in there for 10 000 years in wait for Tantai Jin and Li Su Su.

4. Made sure Ming Ye's Heart Protecting Scale will be left in XiaoYao sect, and in turn Pang Yi Zhi will give it to YBC and XL, and XL will give it to Tantai Jin

5. Made sure Li Su Su will obtain the World Overturning Jade (or World Alluring Jade as some of us call it). He saw Li Su Su will jump from the boat in Mo He river, so the Jade was put there. Also as per his words he knew Li Su Su will take the Jade from inside Tantai Jin,  as he "cannot die yet".

6. Made sure Li Su Su will visit the Barren Abyss in her quest to find a way to destroy the evil bones.

7. Told Li Su Su 1/3 of his plan - "You will need a dream, a thread, and a tear". Not telling her the whole truth is so his plan will not be compromised and fail.

8. Visited Li Su Su's consciousness and reminded her of Ming Ye and Sang Jiu's end. Tower scene is where the last bit is executed perfectly. 

As per this plan, Ji Ze made sure that Tantai Jin will not become Devil God 2.0 and will have a choice infront of him. Ying Yang bracelets could also be a part of his plan, as Tantai Jin will strive to look for YXW's soul while Li Su Su takes her human form 500 years after the mortal arc.

Note: The nails were NEVER intended to kill Tantai Jin, but only weaken the barrier of the evil bones. The scale protecting Tantai Jin was deliberately executed by Ji Ze. The reason why Ji Ze did not tell Li Su Su she needs to insert 6 out of 9 nails in the Barren Abyss is because it could compromise his plan as Li Su Su at that time was not in love with Tantai Jin. The other reason why he kept everything from Li Su Su is because as she fell in love with Tantai Jin later on, she might not be able to insert the nails, hesitate and ultimately fail the mission out of guilt towards Tantai Jin. Ji Ze had to make sure the plan will succeed 100% and could not take any risks. Also, remember his words to Li Su Su and Tantai Jin in episode 13: "You and she both know, but Ming Ye and Sang Jiu do not know." Meaning what he planned and will happen cannot be known by anyone other than him - even Li Su Su and Tantai Jin may not know in the immortal arc. 

 the thing that confuse me and maybe I missed something because initially she had four of the spikes, three dissolved when they got into the argument when he said he killed people after going to the Shang empire originally and she had one left.  Then suddenly she was looking at a lot and I was like when did the rest have time to regrow it never actually showed that which confuse me

 Erin:

 the thing that confuse me and maybe I missed something because initially she had four of the spikes, three dissolved when they got into the argument when he said he killed people after going to the Shang empire originally and she had one left.  Then suddenly she was looking at a lot and I was like when did the rest have time to regrow it never actually showed that which confuse me

The 4 spikes - three dissipated, one came back when they talked in the mausoleum. Then gradually day by day, week by week she got more spikes.

 ColourMePurple:

What about all those charms and protection and other spells she was doing at the beginning? How could she do those as a mortal?

It is power taken from Chongyue (her pendant). It is very limited tho.

 Kiie:

She can do that by writing  some charms on a special piece of paper. Just like Pang Si Ji and Fuyu, they are mortals too. 

Pang Zhi Yi actually ain't a mortal. He has cultivated in the XiaoYao sect. Also the mark on his forehead indicates he is an immortal.