Is it me or does Darth Sidious make you seemingly invincible (figurativeley)?

Depends on who I am fighting. If there isnt someone more dangerous (high DPS) just try to take him out early. Other way is carrying a squad members with high tenacity or Luke Skywalker as leader.

Honestly, I have no idea what tenacity does. I've never seen an explanation of it.

To answer your question, it is you. At least with your current level and heroes.

Second, click on a hero in the character section and below their image is a little circle with three bars, click on that. Scroll to tenacity and it will have a description.

Lastly, Sid is good as noted, but not the best, and easily defeated at higher levels, especially in arena where the match is usually over in 2-3 turns anyway. In GW I usually focus him down first unless, as noted previously, there is someone more dangerous.

Yep, very useful, which is why he's on so many teams. Not sure who are running, but I usually focus him down first in GW, because I aim to take the same 5 guys through GW and having a heal block on them is deadly.
Having fast characters with extra attacks and status effects helps a lot. My GW team now includes Dooku, Daka and GS, usually. Between them, Sid gets one attack on me and he is toast (unless there's someone much more dangerous. If I can't kill him fast, I stun him. If I can't do either I swap out GS for my Sid and try to beat him at his own game.
A counter-attacker like Dooku can help a lot because he likes to AoE early and the counters can knock him down far enough that a striker can take him out.

Welcome to the forum!

Life is easier with Sid!

Also, Sid's heal block doesn't work on Barris' healing ability, as her 'heal' is a redistribution of health across characters.

That isn't entirely true. The first part of the heal works, but the heal itself does not work.

"Widget_gaget;94983" wrote:
Another benefit (or pain if he is on the opposing team) is his heal on any death. Combine that with lumi health up every turn and an ocassional heal, you will have a tough time taking him out if things don't go your way.

If Vader was a bit better, I'd love to try a Sid, Vader, IG88, Lumi, Dooku team. Vader and Sid can lay dots, IG88 can then crush and ability block, while Lumi sits back and heals 'em all. Dooku is just there to counter all the AoEs. :)

There are ways to deal with him, of course. If your team has a healer in it then he needs to be at the top of your priority list for kills. Luckily he's pretty squishy, so this isn't usually difficult unless he goes ninja with the dodges.

If you don't have a healer, then you're probably running a hyper-DPS squad, and you can pretty much ignore him until the opposing team's glass cannons are gone.

LMAO...I was thinking the exact opposite, Sidious dies super fast and easy. I cant wait to replace him. A lot of fights all I get out of him is his AoE, then he countered by Dooku then the opponent AoEs and he dies.