What are Summoning Conditions?
Most monsters can be summoned without any restrictions, even if you might have to tribute monsters to summon them. However, some monsters have special summoning restrictions. Usually, you have to fulfil certain requirements to summon the card. While this can be quite a drawback, most of these monsters have powerful effects to make up for it. There are two types of monsters with summoning conditions; nomi monsters and semi-nomi monsters.
Nomi Monsters
Main Article: Nomi
A Nomi monster will almost always have a very specific phrase in its effect; "This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except" and then says how it can be summoned. Examples include the Berserk Dragon pictured here, Dark Armed Dragon, and Doom Dozer. A Nomi monster's summoning conditions are not always difficult to fulfil; examples include Aztekipede, the Worm Warrior and Yamato-no-Kami; they simply require the removal of a certain type of monster from your grave. However, most Nomi monsters are difficult to summon.
One very important thing about Nomi monsters is that they cannot be special summoned in any way except how it is specified. For instance, if you summon Dark Armed Dragon and it is destroyed, you cannot special summon it from the graveyard with Monster Reborn. To re-summon it, you have to add it back to your hand, and then re-fulfil the summoning requirements.
In addition to these effect monsters, Fusion Monsters and Synchro Monsters with the effect "This card cannot be Special Summoned except by Fusion/Synchro Summon" are also Nomi monsters. Examples include Elemental Hero Mudballman and Trident Dragion, respectively.
Semi-Nomi
Main Article: Semi-Nomi
Semi-Nomi monsters are somewhat more flexible than Nomi monsters. They usually have the phrase "This card cannot be Normal Summoned or Set. This card can only be Special Summoned" and then the summoning requirements. Examples include Fenrir and Dark Necrofear.
The difference between Nomi and Semi-Nomi monsters is that Semi-Nomi monsters can be summoned after they have left the field - however, this rule only applies when they are removed from play or sent to the graveyard. So, a Fenrir that has been properly special summoned can be special summoned from the Graveyard by Monster Reborn if it was destroyed by battle, or from the Removed from Play Zone if removed by Dimensional Prison. However, if it was returned to the deck by, say, Ehren, Lightsworn Monk, it cannot be special summoned by Mother Grizzly.
All Ritual Monsters are Semi-Nomi, and Fusion Monsters and Synchro Monsters are Semi-Nomi unless stated otherwise (see above).
Other Summoning Restrictions
Cannot Normal Summon Or Set
Some monsters cannot be Normal Summoned or Set, but have no restrictions on how they are special summoned. Prime examples include Rare Metal Dragon and Wulf, Lightsworn Beast. The latter gives a method of special summoning, but it never says you must use that method. Thus, you could send either of the two monsters to the graveyard with, for example, Foolish Burial, and then use Monster Reborn to special summon them.
Cannot Special Summon
These monsters are practically opposite the others, because while the others must be special summoned, these must be normal summoned. Examples include all but one of the Spirit Monsters, and the Wicked Gods. These monsters can be even more of a hassle than special-summon only monsters, because of the one-Normal-Summon-per-turn limit.
Inherent Special Summon Effect
Some monsters, such as Gorz the Emissary of Darkness and Cyber Dragon, can special summon themselves when certain conditions are met. Do not confuse this with a summoning restriction. You can tribute summon Cyber Dragon, or discard Gorz and special summon it from the graveyard with Monster Reborn.
Ignoring the Summoning Conditions
Main Article: Ignoring the Summoning Conditions
When a card says that a monster can be summoned ignoring the summoning conditions, it means precisely that. You can summon it without interference from any conditions. A perfect example is Level Up!, which allows you to tribute a Horus the Black Flame Dragon LV6 to special summon Horus the Black Flame Dragon LV8, without having to destroy a monster by battle. Another example is Ultimate Ancient Gear Golem.
