Altcoins generally carry higher volatility and higher correlation to Bitcoin on the downside than the upside. When bitcoin-dominance rises, altcoins usually underperform; alt season is the reverse.
The long tail of altcoins is where rug-pulls and pump-and-dumps live.
Example: in a month where Bitcoin falls 20%, a mid-cap altcoin might fall 45%. In a month where Bitcoin rises 20%, the same coin might rise 15% or 80%.
Related: bitcoin-dominance, rug-pull, volatility, pump-and-dump