Lay Waste is very strong at farming minions and harassing enemy champions.
Ask your allies to help point out when you should use Requiem to get kills in different lanes.
Rammus often stacks high Armor, leaving him especially vulnerable to caster damage while not in Defensive Ball Curl.
Pay particular attention to when his Defensive Ball Curl is off. Rammus has much lower stats than a normal tank when he's out of the stance.
The stat comparisons provided here show several critical Karthus versus Rammus matchup stats that can help you understand the differences and similarities between this pair of champions. As an example, Karthus’s KDA ratio ([kills + assists] / deaths) of NaN is better than Rammus’s KDA ratio of NaN, highlighting that Karthus may be more central to his team's team fighting effectiveness than Rammus..
Karthus normally has a slightly larger longest killing spree than his foe does. On average, he takes less damage than Rammus. This often reflects different amounts of tankyness, but it can also indicate that the champion with higher HP has less mobility and thus is unable to kite away from additional harm when engaged or poked.
Both League champions are great. Both champs have their pros and cons. In League's current meta, Karthus usually loses when taking on Rammus, with a 48.3% win rate. As a result, Karthus makes a poor counter for Rammus.
While Karthus does have a lower win rate than Rammus, when facing one another, Karthus also has a greater level of difficulty that makes him a more complex character to develop with. You still need to be cautious when picking Karthus into Rammusas his relative depth means you may not be able to unleash his full potential without a lot of practice beforehand.
Moreover, Karthus also has some amount of CC and other utility, a similar amount to Rammus. This makes her just as valuable during teamfights, especially when facing champions with a lot of burst damage.
While there isn't one best champion in League of Legends, in Karthus vs Rammus matchups, Rammus is the better champ with a lower win rate, more champion depth, and a similar amount of utility to help out your allies during late stage team fights.
Karthus is a somewhat poor counter for Rammus. You will do well by focussing your gameplay on keeping up your gold income and taking out objectives. If you do that, you should do very well as Karthus against Rammus.
To truly master Karthus to counter Rammus during both the lane and mid / late game phases of League of Legends, you should keep reading to learn a few extra tricks and insights into this matchup. If you listen to the build and tips displayed above, you will grow your win rate significantly and be closer to League of Legends pro players.
Karthus usually racks up much more CS as Rammus. Champs who on average don't take much CS typically don't have to have much CS to be effective, such as supports. They are able to scale well off of their abilities and first items alone. Yet, champs with large amounts of CS, such as hyper-carries, often require a lot of items to be effective. In either situation, try to do better than the numbers shown here to do well.
The best items to have in your Karthus versus Rammus build consist of Liandry's Anguish, Rabadon's Deathcap, and Shadowflame. When Karthus included at least these three items in his build, he performed a lot better when fighting Rammus than with most other typical item sets. In fact, Karthus had an average win rate of 48.3% when countering Rammus with this counter build.
To have the greatest likelihood of vanquishing Rammus as Karthus, Karthus players should take the Dark Harvest, Taste of Blood, Eyeball Collection, Ultimate Hunter, Presence of Mind, and Last Stand runes from the Domination and Precision rune sets. Out of all the rune combinations players picked for Karthus vs Rammus matchups, this mix of runes yielded the highest win rate. Notably, these runes averaged a 48.3% winrate overall.
By default, tips, stats, and builds on how to beat Rammus as Karthus are given for all ranked divisions combined. If you want to scope the stats and builds to an individual skill level, you can use the selection menu located earlier on the page.