When it refers to the defenders, they are creatures that usually have a high defense, which they characterize that in the majority they can not attack, exempt some that by some restriction they are allowed to attack.
To perform the combo you need to have minimum creatures in field 5 and 4 of them that are defenders. For this combo you need 2 particular cards, which are:
In order for the combo to be made, you must have these two (2) cards matched with the ability of the galvanic alchemist, which does, by paying two uncoloured and one blue mana, both creatures are righted and with the ability of the Breaker Guardian axes, that when turning, generates mana of any type, for each defender you control, when you perform the skill the 2 skills together and have 4 defenders, with 3 of the 4 mana you pay the skill of the alchemist and there is a mana remaining in the mana pool and this ability can be repeat it endlessly and thus generate infinite mana. To make a play and win the match.