Read this entire guide (including Gearing) before you decide to build an infinity team. There are a lot of moving parts and you need to understand how they all work together before you can build a team that will work. Once you know what kind of team you want to build, then make sure to fully read the guide for that specific team as well.
The idea behind an infinity team is to exploit an interaction between Underpriest Brogni and Corpulent Cadaver's abilities to do massive damage with Cadaver's A1 ability.
Cadaver's A1 damage will have his current shield value added to it, and its direct damage is not subject to crit damage multipliers, weak hits, or even poison cloud damage.
Brogni's A2 will increase the value of all allies shield by 30% of the damage he inflicts. The idea is that you will be growing the shield faster than it can be depleted by damage, and thus continually increasing Cadaver's damage throughout the entire battle.
One very important point: Cadaver needs a non-protected artifact shield as well. Brogni's A2 will grow BOTH shield at the same time, so by having a second shield buff you are going to quite literally double your damage for the run.
This shield can be provided by either a divine set on Cadaver or a normal Shield set on another member of the team. The shield value does not matter, only that it is there.
In order for this to work, you need at least one additional thing: the ability to increase buff duration faster than Cadaver takes turns. This requires either a single buff extender with double Yumeko to keep abilities ready, or 3 buff extenders at slightly higher speeds (depending on cooldowns, you may need to go even faster or slow Cadaver down).
Once you have these pieces all together, your damage will start to quickly ramp up to the point that Cadaver is one-shotting new Hydra heads (through New Head protection!). Near the end of Nightmare runs you can see hits (+hex splash damage) exceed 100m damage for a single Cadaver hit.
There is no full-auto for this kind of team. These teams require extensive manual setup. Only once Cadaver is one-shotting Suffering, can you then put it on auto if you have the Skill AI set up, but you will need to click on heads to manually target the live heads to make sure that they are focused over the stumps.
Because Brogni will appear to have the most damage on your team, he will receive the Mark of the Hydra debuff at the beginning. This is OK and you should expect to see him get eaten! Once he gets eaten, you should have ramped your Cadaver damage up enough to get him out of the stomach in a single hit. Once you have him back, re-apply whatever buffs you can and continue as normal.
Except for Cadaver's shield buffs, any other buff can be stolen or run out- just make sure to replace them when you can. Once cadaver is one shotting, you don't even need a shield on your other champs.
Even with all the hex mitigation, you're going to end up in situations where you can't land it on him and he takes turns. This is where your Mischief tank champions RES is super important, but remember there is always a ~3% chance of still stealing buffs. This will happen, and it might end a run. Remember this is normal, and you should expect to have to restart a few times especially while you are getting used to the team.