Glad to help :)

Su.Ki you're amazing!

Here's an important rule:

1. Look at the following conjunctions:

2. Remember that when we use these words in future sentences, they need to be followed by a present - either present simple or present perfect - tense, not a future tense.

'He's going to get mad when he sees the other animals.'

not

'He's going to get mad <s>when he's going to see </s>the other animals.'

We won't have dinner until you get home

not

We won't have dinner <s>until you're going to get</s> home.

I'm going to have a big party if I pass my exams.

not

I'm going to have a big party<s> if I will pass</s> my exams.

Learn this rule and remember it - it's a key aspect of English grammar.

"He's going to get mad when he sees the other animals" sounds the most natural. The word "when" indicates that it is in the future.