Puncturing Taunt can be used on enemies pushing your turret to make them attack you and causing the turret to attack them. It can also be used to take the focus off more squishy allies, allowing them to deal more damage than they would have had they been the focused target.
Puncturing Taunt can also be used to "pull" enemies towards your team as an enemy will be forced to get into attack range to hit you. This is more effective with melee champions whose attack range is shorter than ranged ones.
When using Tremors, you can use all your spells to keep enemies in range of this spell in order to maximize damage. This is possible because the ultimate is not channeled.
Tremors affects turrets, making Rammus a very good pusher, especially late game when he can tank the turret for his team.
Backdooring is a simple matter because you can easily use Powerball to run away before enemies catch up.
Rammus can use Tremors while using Powerball, making it very useful for destroying towers or champions that are low on health and escaping.
Randuin's Omen in conjunction with Puncturing Taunt and Defensive Ball Curl allows you to slow the enemy team heavily and make chasing easier. However, it reduces the enemies attack speed so they won’t get as many reflected hits off you when you taunt them
Thornmail is a very effective item on Rammus, as it reflects damage from auto-attacks (which the enemy is forced to use during Puncturing Taunt) as well as stacks with the reflecting damage given during Defensive Ball Curl along with a lot of attack damage due to his passive.
Rammus is a strong jungler, with exceptional ganks. Powerball allows him to initiate ganks suddenly, and Puncturing Taunt is a strong CC ability with a fairly long duration.
Note that Rammus'sPowerball, whilst it still does damage, it has no crowd control effect on Baron Nashor or the Dragon. Also note that Puncturing Taunt now has absolutely no effect on Baron or Dragon (it will not reduce armor or force either to attack you). Both skills will still affect all other neutral creeps as normal.