When a special summon occurs in face-down defense position (like Cyber Jar, Shallow Grave, Nimble Momonga, Bubonic Vermin, etc.) is it considered summoned? because I heard that face-down cards are NOT considered summoned.

... and can I use Torrential Tribute, Horn of Heaven at the time they are summoned face-down?

... in addition, can I use "Jowgen the Spiritualist" to wipeout those face-down cards, since they are Special Summoned by an effect.

... lastly, if multiple summons occured at one time (Cyber Jar, Shallow Grave, Nimble Momonga) what will happen if I use "Horn of Heaven" or "Bottomless Traphole", will I have to choose only 1 monster to negate/destroy?

Many thanks in advance...

1) No you cannot, it's exactly like using Torrential Tribute on a face-down Normal Summon.
"Torrential Tribute" can be activated after a monster is Summoned through another card’s effect, such as "Monster Reborn", "Scapegoat", "Cyber Jar" (if Flip Summoned, not set), or "Call of the Haunted".

2) When playing with this card you need to remember which monsters on the field were Special Summoned because they can later be destroyed with the effect of "Jowgen the Spiritualist". If a monster that was Special Summoned is flipped face-down, it can still be destroyed by the effect of "Jowgen the Spiritualist".

3) BOTTOMLESS TRAP HOLE:
This card can remove from play multiple monsters at once, if they are Summoned simultaneously. Since this card can affect multiple monsters, it does not target.

1. You CAN use Torrential Tribute or Horn of Heaven on a Special Summon face down monster, this is STILL considered a Special Summon regardless.

2. Yes you can use Jowgen's effect to wipe out face-down special summoned monsters.

3. Given that Cyber Jar was flipped summoned, Bottomless will remove all that are 1500+, for Horn of Heaven you can only select 1 monster.

When a special summon occurs in face-down defense position (like Cyber Jar, Shallow Grave, Nimble Momonga, Bubonic Vermin, etc.) is it considered summoned? because I heard that face-down cards are NOT considered summoned.


No, they are considered Special Summoned...the only time monsters are not considered Special Summoned is if the card does not specify (like Dimensionhole, Strike Ninja, Interdimensional Matter Transporter, etc.

Otherwise...whenever it says to Special Summon in face-down Defense...it's still summoned.


... and can I use Torrential Tribute, Horn of Heaven at the time they are summoned face-down?

No


... in addition, can I use "Jowgen the Spiritualist" to wipeout those face-down cards, since they are Special Summoned by an effect.

Read above post


... lastly, if multiple summons occured at one time (Cyber Jar, Shallow Grave, Nimble Momonga) what will happen if I use "Horn of Heaven" or "Bottomless Traphole", will I have to choose only 1 monster to negate/destroy?

Horn of Heaven will only work on 1 monster...

Bottomless can remove multiple monsters if they are 1500+ ATK and Special Summoned face-up. If they are Special Summoned face-down, then Bottomless Trap Hole cannot "tell" if it is 1500+ ATK or not because face-down cards are "blank".

Half you need coffee :), this was discussed a long while ago, yes you can:

http://lists.upperdeck.com/read/messages?id=5608#5608

Yes I do...this is what happens when you post on 2 different forums while reading a 3rd (the other 2 having WORSE questions/"combos"/"discoveries"/etc than here)