Temperature Manipulation.
Out of all the powers that Alex has right now, he considers this one as this weakest.
After all, the ability to change temperatures on a whim is not a really useful power, especially against Sixth Stage Beings.
How would making a metal hot or cold allow Alex to defeat an Immortal Stage practitioner? Most likely, an Immortal will just shrug these changes off with his/her power. The same case also applies to other Sixth Stage Beings.
With their bodies able to turn into energy or essence at will, the most damage that Alex can give to these Sixth Stage Beings could only be minor inconveniences to them….
If this was the only problem with Temperature Manipulation, then Alex can still manage to do something about it. However, there is another limitation that is much more bothersome than this power's weakness.
Lol, now I am imagining Alex creating earthquakes out of nowhere.