The Toad from X-Men: Days of Future Past (Evan Jonigkeit) is supposed to be a younger, darker version of the Toad from X-Men (Ray Park).
From an interview with Evan:
Jonigkeit, a fan of the books, will very likely have minimal screen
time and dialogue [in X-Men Days of Future Past] – sadly like most of the characters we know about –
but he does confirm that his Toad does setup the Ray Park version from
the original X-Men, but is quite a bit different.
”I read a lot of the comic books. I found out the storyline of my
character, who is Toad. X-Men fans will know that Ray Park played him
in the first movie, so it’s a generation story of how he came to be.
It’s really cool.”
“The aesthetics of the character are much different, and I’m not
really allowed to say a whole lot more than that,” he said. “It’s
darker. I would say it’s a darker tone.”
Apparently the original actor (Ray Park) was supposed to be in X-Men 2, but scheduling conflicts led to his mutant being written out of the series in X-Men 1.