It should be the altcoin that is not yet pumped to surpass ATH.
I can't give you the name of altcoin but you can try to take a look at the top 100 coins and you will be seeing it which altcoins that is not yet pumping. I think that can be searched easily when you wanna spend your effort to find that on CMC.
From my experience here, I would say that this is the wrong strategy. If a particular altcoin is not going up when the others are getting pumped, in all probability that may be due to the fact that it's development is stagnant. So there is a very good chance that you will lose your capital in case you make an investment with such coins. So unless you have a solid reason to make an investment with such altcoins, please stay away from them.