SC2Mapster

Use a Behavior type ability that is levelled that uses Buff behaviours with a damage response with a % chance to work that reduces the damage on defender to 0%. The Combat: Damage Response - Modify Fraction field is the one you want.

Under the Units data type:

The Armor Formula for life, energy and shield

Revive Cost

Tactical AI Range

Tactical AI used

Hit Test Priority

Subgroup Priority

Revive Cost Per Level

Cost

Acceleration 

Collision flags and radius

The Mover used

Turn Rate

energy and shield regeneration

Mass

Repair Time

Vision Height

UI Description (tooltip)

Random Names

UI Subtitle

the Unit: Effect on birth death create and revive

Idle Command

Loot

Under the Move ability: 

Smart Priority

Follow Filters

Move Filters

Under the Attack ability:

Smart Priority

Supported Filters

Under the Morph abilities:

Cancel Unit

Default Button

Button Requirements

Command flags

everything in the Ability: Info array

UI Activity tooltip

That is not even starting with the weapon and actors.

Go to the data editor and look at all data types associated with the unit. Those with a ^ next to the field name can be upgraded.

For a start SC2 uses Galaxy not Jass (the trigger language of WC3).

To do random chance you will use a Set Variable action definition to set an Integer type local variable using a Random Percent function. You will then have If Then Else action definitions that use Comparison conditions to compare the value of the variable against a Arithmetic (Integer) function of 100 minus a global variable of the Integer type which is your percent chance using a greater than or equals comparator. That way if the random value is larger than the other number it will do your desired actions. If you are storing your units in an array this process could be built into a For Each Integer loop using a second local variable of the Integer type which is used in the loop to correlate unit type with the percent chance.

For the dialogs I would use Label dialog items and Set Dialog Item Text actions that use a Combine Text function and a Convert Integer To Text function. That way you can use your variable for the percent chance to adjust what is displayed next to the fixed text for the unit type.

Use a requirement. OneTwoSC had a video tutorial on this at one stage. Or look at my symbiont demo map since I used the same requirement setup to determine host/item interaction.