Excalibur, after Mumm-Ra uses Arthur’s sword to stab the Eye of Thundera (it also disappears from the other cats’ badges too).
The Thunderscope, again due to an (apparently fatal) encounter with Mumm-Ra.
Can’t think of any others.
Correct on both counts, Liam! 
The second time it was thanks to the Mumm-Ra being armed with the Sword of Plun-Darr.
However, there is still at least one more answer that I know of (maybe more that I don’t know of). So I’ll wait for a couple of days and see if anyone can give us more answers. If not, you will be the winner 
Looks like there isn’t anybody else replying so I hereby declare Liam as the winner! Your turn to give us a new question, sir!
BTW, for trivia buffs, the third answer was in “The Shadowmaster”, when the connection between the Sword of Omens and the Book of Omens was broken.
OK then. Coming up with trivia questions from a finite source such as this gets tricky after a while, but I’ve got one:
The Thundertank’s rear doors normally open in their entirity, but there’s one occasion I can think of where instead of the top opening completely, just the Cat symbol opened. What was the episode?
I think the episode is “Trapped”. Lion-o uses the claw to hook onto Mummra’s cape.
Correct! Your turn, Mongor!
New Question:
What episode shows windows in the back of the Thundertank?
Return Of The Driller?
Turmagar the Tuska.
It is Turmagar the Tuska…it’s your turn Mark M.
New Question:
Name the first weapon we see get broken and the episode.
The first TC weapon, or any weapon?
Only the Sword of Omens comes to my mind in “All that Glitters”, but I guess it’s not that easy lol. I can only think of the kittens’ lassos…
Although I think Panthro’s nunchucks got broken once (maybe I’m making it die to the question, because I can’t remember if they indeed got broken, in which ep, or if it was previous to All that Glitters).
Any weapon. I am afraid all your answers are wrong though.
In “Exodus”, as Panthro delivers that memorable line, “if you guys were as mean as you were ugly,” he shatters a Jackalman’s mace.
Correct Liam. Your turn.
OK. I’ve got one. Took a while to think of one, as we’ve exhausted so many areas of trivia. Anyway, here it is:
Despite having the usual four limbs, Slithe was once referred to as a snake. Who described him so (and in which episode)?
I’m sure it was a villain… I’m torn between Mumm-Ra and Ratar-O (of course, it can be none of them).
To the best of my knowledge, neither of them ever made such an analogy.
Then I know nothing 
Wasn’t it Hachiman who said :“Let me finish this worthless snake!” when referring to Slithe in The Thunder-Cutter?