Mystic Knights of Tira Na Nog was made by Saban and aired from 1998 to 1999. It was the first live-action Saban series, other than Next Mutation, that did not use Tokusatsu footage. It was shot in Ireland and in Germany, it had a better different theme song than we heard in the US. There was a rumored second season called Battle Thunder. The official logo below, so it did go enough pre-production to have a logo. Some sources say they saw prototypes for the toys and that production even started.
This website above claims to have a new Knight, Seanin, the Mystic Knight of the Swamp.
From the site: "Seanin was discovered from the same piece of scroll, that the rest of the knights were foretold in. Only one thing is different, Seanin is evil. Queen Maeve learns of him and decides that he will be perfect to fight against the good Mystic Knights. Seanin's elemental call is Death Below Me. His weapons is a wicked scimitar and his armour is steel plate and chainmail."
"Also from site: Joseph Barton, a 23 year old, was born in Atlantic City, NJ in 1975. (Meaning this was written in 1998.) He grew up in Galway, Ireland, taking an interest in fencing at the age of 10 (and eventually began a study in the arts as well. Among his talents are irish stepdancing, singing and acting. He speaks French, plays piano and the Uillean Pipes, and has performed in several musicals in Dublin and Britain. "I haven't had any major roles," he mentions in an online interview in January, but his Mystic Knights role is sure to raise his profile a little more. Joseph shared a few thoughts on his newest gig as Seanin, commenting "I think the writers figured Maeve didn't have a shot with 5 knights against her." He describes Seanin as "a villain.", "quite unique", with armor made of real steel instead of the fiberglass used in his castmates' costumes. "[Steel is] more evil looking I guess," says Joseph. "..don't feel bad if you don't like my character." Seanin is apparently as evil as they come. He sounds like the kind of guy his fans will love to hate. Look for Seanin, the Mystic Knight of Swamp to debut in the Mystic Knights of Tir-Na-Nog this fall."
And sadly, it never happened. But no knowledge if this is official. It could be fake and be online since 1998. I never saw it but I did know about the logo. As you can tell, there is very little information about Mystic Knights second season. I liked Mystic Knights even though it wasn't accurate celtic fantasy and had lots of recycled monsters from past Saban shows. Some sources has 'Death Below Me' as 'Swamps Below Me' which makes more sense. But from the picture, he doesn't look so 'swampy.'