These are the different leagues in PoE:
Typically, "hardcore mode" in action RPGs involves permadeath. A character killed in this mode cannot be accessed any more. In Path of Exile, slain hardcore characters revert to the parent non-hardcore league. This system encourages non-hardcore players to try the hardcore game mode, while still permanently removing hardcore characters from the economy when they die.
In Ironman, players are unable to trade with vendors or refill their flasks in town. Mana regeneration is disabled by default. Players are encouraged to band together and manage their resources in order to survive.
The cut-throat leagues appeal to the niche of players who demand the most hardcore gaming experience possible. In this mode, all world areas are public, with full PvP enabled by default. Slain characters drop all their items upon death. This game mode can also be combined with Hardcore to create an even more unforgiving world.
An attrition league is a short duration league that starts with a fixed number of players and eliminates the player with the lowest amount of experience at periodic intervals. For example, a 24 hour attrition league might start with 100 players and eliminate one player per 12 minutes after a four hour initial leveling period. Players would be able to see how close to elimination they are on an on-screen ladder display.
On a side note. I'm experimenting trying to make a witch summoner. I'm gonna pick up all the +minion skills, and also shoot for Minion Instability (the one that makes minions explode and deal aoe fire dmg when low on life). Anyone have experience with such a build and how well does it work? I've always been a pet class type person...so I wanted to create something revolving around that.