The player must play at least one card to the field after drawing. Cards can be "fused" in the hand without the card Polymerization; the player can fuse any amount of his or her cards together and in any order, but the chance of a "successful" fusion (where a new monster or magic or trap is made, or when a monster is strengthened) depends on the cards the player is fusing. After fusion, cards can only be played face-up. Traps that are played face-up are not activated until their condition is met, but those produced as a result of fusion are immediately activated (often to no effect). When any magic or trap card is fused with a monster that is not compatible, the magic or trap card is discarded and the monster is unaffected. Playing ritual cards to summon ritual monsters requires specific monsters to be on the field in order to work; for instance, "Serpent Night Dragon" is summoned by playing Revived [sic] of Serpent Night Dragon while Darkfire Dragon, Dragoness the Wicked Night and Obese Marmot of Nefariousness are in play; this differs from the rules of Ritual Spell Cards in the TCG, which simply requires tributing monster cards with combined levels equal to the Ritual Monster. There is no Special Summoning; fused and ritual monsters are simply considered normal summons. Monster cards must select one of two "Guardian Stars", which allow a monster to gain five hundred attack and defense points if it has chosen a superior alignment against its opposing card; these alignments are taken directly from cosmic bodies and are arranged as follows (> means "is superior to"): Mercury > Sun > Moon > Venus > Mercury Mars > Jupiter > Saturn > Uranus > Pluto > Neptune > Mars The following example is used in the manual: "when "Gaia the Dragon Champion" (AP:2600) chooses Mercury and attacks "Blue-Eyes White Dragon" (AP:3000 and in attack position), "Gaia" has his AP increased to 3100, making it possible to defeat "Blue-Eyes White Dragon"." The Guardian Stars selected represent the type of the monster. In the 3-D battle sequence the attack the monster uses depends on the guardian star selected. For example, when you summon Meteor-Black Dragon you are given the choice of Sun or Mars. Choosing Mars will cause Meteor-Black Dragon to use a fire attack and give it an attack bonus against Jupiter (typically plant-type) monsters.