Mostly rhymes with:
ghostly, astley, costley, costly, dishonestly, earnestly, firstly, ghastly, ghostly, honestly, justly, lastly, manifestly, modestly, priestley, priestly, robustly, steadfastly, unjustly, vastly, westley
Mostly sounds like:
macdill, macdowell, machtley, macktal, magdala, mastel, mcdeal, mcdill, mcdole, mcdowall, mcdowell, megadeal, migdal, mightily, minoxidil