Did Shredder know what the mutagen was?
 

The reason stated for dumping the mutagen into Yoshi's lair was to "destroy" him. This makes me wonder if he even knew what it was, here are the following possibilities:

1. He knew what it was and hoped for the best scenario
2. He had mistaken it for some kind of poison
3. He had no idea what it was and just wanted to see what would happen

In the first one he's just stupid, he would have known full well Yoshi could turn into something dangerous and did it anyway. In the second one he's not necessarily stupid but certainly incompetent. In the third he should have done some labratory experiments first. None of these answers are really satisfying because they all rely on Shredder being clueless about his own murder weapon to some extent.

I think something that is consistent in most of the incarnations is that when Shredder is blinded by rage, he can become incredibly destructive, and doesn't really think straight. Take 2012, for instance, when he chose to kill Splinter even when it meant the world would get destroyed.

I'm guessing he didn't know what the mutagen did, and just chalked it up to being a poison that would kill or greatly harm Yoshi. He didn't care what it did, he just wanted Yoshi to suffer.

I figured Shredder thought it would either kill him outright, or turn him into some sort of monster that would hunted for the rest of his life.

I mean even if Shredder knew he would mutate into something, he was most likely not planning on Splinter maintaining his intellect and overall personality. Imagine if Yoshi turned into some giant feral rat monster. He'd be hunted down and killed by New Yorkers within the month.

Iknew it because Krang had told me and it was him who gave it to me! I thought that the world will kill him after he becomes a monster. That would be much better than if i killed him when he was a human because now thath e is a monster i know that most people are fearing him and want him dead.

Splinter was human not Krang. I said that it is better for me to kill him now that he is a mutant rat than kill him when he was a human, that what i said.