How do you make a water mob that attacks player and some more questions

please answer??

It says 

Executing gradle task: build
Build info: MCreator 2020.1.05419, 1.12.2, 64-bit, 16315 MB, Windows 10, JVM 1.8.0_232, JAVA_HOME: C:\Program Files\Pylo\MCreator\jdk
This mapping 'snapshot_20171003' was designed for MC 1.12! Use at your own peril.
:deobfCompileDummyTask
:deobfProvidedDummyTask
:sourceApiJava UP-TO-DATE
:compileApiJava NO-SOURCE
:processApiResources NO-SOURCE
:apiClasses UP-TO-DATE
:sourceMainJava UP-TO-DATE
C:\Users\(my username\MCreatorWorkspaces\cenozoicraft\build\sources\main\java\net\mcreator\cenozoicraft\MCreatorHyneria.java:72: error: incompatible types: EntityCustom cannot be converted to EntityCreature
         this.targetTasks.addTask(1, new EntityAIHurtByTarget(this, true));
                                                              ^
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error
:compileJava FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 0s
5 actionable tasks: 3 executed, 2 up-to-date
BUILD FAILED
Task completed in 2444 milliseconds

bump