Rammus, the Amordillo is a late game tank with a lot of CC and the speed to make Sonic cry. He boasts a thornmail-like ability in his kit, the "Thousand Year Taunt" and an AOE damaging ability that can turn an entire teamfight in his teams favor. A good rammus will look to snowball his teams lanes ahead or countergank the enemy jungler with all the CC he has and will become an unkillable taunting machine in the teamfight phase
Passive – Spiked Shell
Rammus permanently has bonus attack damage equal to 25% armor.
Q – Powerball
Rammus tucks into a ball and begins to roll for up to 7 seconds, losing the ability to use basic attacks or use Puncturing Taunt but amplifying his movement speed by an additional 20% each second, up to a maximum 140% increase
Upon colliding with an enemy, Rammus Airborne icon knocks back all nearby enemies, dealing them magic damage and Slow icon slowing them for 2 seconds afterwards, also ending Powerball in the process.
Powerball can be canceled instantly by reactivating the ability, or 1 second after activating Defensive Ball Curl
W – Defensive Ball Curl
Rammus drops into a defensive stance for 6 seconds, gaining bonus armor and magic resistance, as well as dealing magic damage to enemies whenever they use basic attacks against him.
Activating Powerball ends Defensive Ball Curl's effects after 1 seconds.
E – Puncturing Taunt
Rammus taunts the target enemy and reduces their armor
R – Tremors
Rammus creates an earthquake around himself for 8 seconds, dealing magic damage to nearby enemies and enemy structures each second for the duration
Like most tanks, Rammus isn't actually a tank early, and by virtue of his passive, he doesn't do much damage early either. Playing a heavy counterjungler like Lee Sin or Elise means that you can put him behind really easily
Defensive Ball Curl has a long cooldown, and when it's inactive Rammus has lower stats than most other tanks. This is a rare time when killing the tank is easy. Preferably with ranged champions though, so that no one gets taunted.
Rammus will spend the early game stacking armor because of how important Thornmail is to him. This means that champions that do a large amount of magic damage make him vulnerable, forcing him either to delay his thornmail, and thus a lot of damage, or to be not-very-useful against the damage he has to tank.
Lee Sin kills him early, peels him with Dragon's Rage and can kick his carries into your team. Until Rammus gets a decent amount of armor, Lee Sin abuses this guy with burst and execute damage and high early game pressure on his lanes.
High burst magic damage with a large amount of mobility with a strong early game. Rammus can't compete with her, she'll just kill him a lot early, then pressure his laners into losing lanes and snowball the game
This guy's just a good counterjungler. He can take Rammus' camps and kill Rammus too, and in the time it took him to do that, Rammus would have only been halfway done with the camp in question. He can keep up with Rammus and has the option to do a lot of magic damage, totally bypassing the fact that Rammus loves armor, or opt for Turtle stance and completely ignore the minor damage Rammus does in the early-mid game
Kindred just hurts. Nerfs or not, Kindred really hurts. She also can just kite for a long time, by the time that Rammus can taunt her in a one on one, the fights practically over. The early game is just a pain, and in the teamfight phase, she can run down Rammus' ultimate timer with her own ultimate, mitigating at least a part of his damage.
Build mixed protection. Armor for his passive damage, and MR for his ultimate, he won't do a lot of damage later on, at least not in comparison to the AD Carries, but in the mid game he can actually be a powerful damage threat. Buying at least a spectre's cowl is worth the cost to reduce the damage done by the Thornmail he'll buy early as well.