you don't get it at all.
Extra attack isn't +1/+0, the extra attack is that creature attacks one more time.Example: you have jade dragon 12/9 and you use strength bite on, jade dragon attack and cause 12 damage to opponent and attacks once more causing 4 damage.
If you use strength bite on the same creature twice it will attack just one more time and will be healed every turn by 2.
tiny critter can use this skill just once like deja vu
It's like little of adrenaline and little of healing together