Here's a nice sentence making worksheet on Mixed type of conditional clauses. Student just need to read the situation to make up appropriate sentences using mixed conditional, which summarizes the situation in short.
encourage pairs to check each other's worksheet
The answers to each question can be expressed in different ways, so be ready for different approaches and explanations to each question. I think letting students check the answers in pairs is a brilliant way of utilizing this material in your ESL class. It'll start fruitful discussions for consolidating Third Conditionals.