"Lol" is a modern internet slang term that doesn't have a direct equivalent in Welsh. However, depending on the context, you could use:
* Ha ha! (for a simple laugh)
* Chwerthin! (means "laughing" - could be used as a response to a joke)
* Dyma'n ddoniol! (means "this is funny!")
* Waw! (an expression of surprise or amusement)
Ultimately, the best way to express "lol" in Welsh depends on the specific situation and the intended meaning.