Those Classicists and their preoccupation with scansion! Ideally, a limerick would have the correct metre all the way through; but as the Moderator says, this is for fun. There is a way to read the current poem aloud and make it scan, by putting emphasis in certain places and pausing in others, so I personally don't perceive a problem with it.
When the team met Lord Fear
Treguard muttered "oh dear"
For they'd come so far
With a fake silver bar
When Simon's team found Block and Tackle,
They heard a mysterious cackle.
As Grotbags appeared
Just as they had feared
And zapped them 'til she heard them crackle.