I would simply use Dark Ages rules. In Dark Ages a shield possibly:
- Lowers difficulty of active parry (defensive action) of the shielder, the lighter the shield, the lower the difficulty to parry. For example, a small round shield (a buckler) lowers this difficulty by 2.
- Gives passive defence against melee and/or missile attacks against the shielder by raising difficulty of the attacks. This is essentially the same as being behind a cover. For example, a kite shield increases difficulty of attacks with both melee and missiles by 1.
For slow projectiles, such as thrown stones, or if you have Celerity, you could probably even try to actively parry a projectile, with Quickened Senses combo discipline (Auspex 1, Celerity 3) you could probably even parry a bullet.
Ballistic shields are relatively heavy, so I would make actively parrying with them (if you don't have another weapon) even harder (+1/+2 to Difficulty) unless a shielder has a sum of Strength and Potence of at least 4.
I would agree with Space Ostrich in that shields can be treated as cover against missiles, as listed on page 278 of V20 Corebook. Dark Ages basically offers the same thing (increases difficulty to hit you).
Shields, even ballistic, differ in size. Some only cover your torso, some can be treated as "only head exposed" (+3 difficulty to hit for the opponent) if not as +4, as some shields don't even expose your head. Keep in mind that 10 is always a success result anyway. However, because ballistic shields are especially designed as cover and normally have designated observation slits and firing holes, I wouldn't add any penalty to the shielder (just like using a shield in Dark Ages). If the shield covers you fully and you are not shooting at the moment, hitting you from the front would be totally impossible.
As one of your hands is occupied, you can't use a weapon that would require using both hands, such as a sniper rifle, only a pistol or a small SMG would be OK. Or a katana. :3
Ballistic shields are a very resilient device, I didn't happen to find a test video which would show some weapon's ability to penetrate it, even AP 12-gauge bullets didn't succeed. I would assume that some very, very heavy guns like stationary high-caliber machine guns would penetrate them, but this is nothing more than an assumption.
Riot shields, on the other hand, are light-weight and don't always offer protection from firearms (though, some protect their user from handguns and ordinary shotgun slugs). If a shield is hit, I would simply add several dice to target's soak pool depending on shield's resilience, but make parrying difficulty relatively low, they are as easy to use for melee combat as medieval shields if not better. The same story with soak dice would go if trying to penetrate a ballistic shield.
A riot shield is something like pavise shield of modern days, so I would apply the same rules for both. Sadly, I didn't manage to find the stats of pavise shields.
Best Answer
(The stats that I decided to use are at the end of the answer, right after the reasoning)
After consulting my friend who is a veteran WoD player, who suggested to look for the answer in Werewolves book, I actually found it.
Level 5 power of Elemental Mastery allows a vampire to summon a spirit and, with enough effort, control it, most likely also forcing it to materialize.
So, let’s learn about how do they work. V20 Corebook of Werewolf: the Apocalypse describes spirits in general on pages 365-368, and elementals in particular on page 370. A brief introduction into how spirits work will be needed now.
Instead of Traits that most characters have, like Strength or Intelligence, they only use Willpower and 3 unique Traits: Rage, Gnosis and Essence. Spirits use (and roll) Willpower if a normal creature would roll Dexterity or Stamina, for example, to soak damage (they can soak any type, even aggravated), to dodge (they have to split dicepools if they dodge and attack in the same turn), to check if the strike hits. Rage is used for Strength rolls, and Gnosis substitutes all Mental and Social Traits. Essence is like spirit’s health and mana: they spend it when using special powers (“Charms”) and lose when failing to soak damage. Spirits don’t naturally die when Essence drops to zero, but just fade into the Umbra. Essence is normally the sum of Willpower, Rage and Gnosis.
The “The elemental has three dots in all Physical and Mental Attributes.” sentence can be possibly understood as spirits having Willpower, Rage and Gnosis of 3 and, hence, Essence of 9.
Let us list elementals covered by the book with their appropriate stats and Charms. Quoting the book, “Elementals vary wildly in power, from the minor Gafflings in a candle-flame to the Incarna-like power of the water in an ocean. The following Traits apply to minor elementals:” So, even those Traits are considered weak by WtA.
With this power, an elemental with WtA stats has 14 soak dice (9 without it), soaking 5,6/3,6 levels of damage on average, and with VtM stats he will have 6/3 respectively, averagely soaking 2,4/1,2 levels of damage.
I would assume that the thaumaturge may force an elemental to materialize. Also this power is assumed to be availabale for all spirits, and for some particularly strong it gives more health levels than creatures traditionally do. Do not that it makes Essence unimportant as health, only as mana.
Unclear if the elemental has to roll to hit with this (most likely not, as it's an AoE power). WtA and VtM elementals would both roll 2 dice.
WtA elemental rolls 7 dice with a chance to succees of 99%, 90%, and 55% respectively, VtM elemetals roll 3 dice for 92%, 74% and 39%.
VtM elemetals roll 3 dice for 92%, 74% and 39% chances to succeed. WtA elemental rolls 5 dice for 97%, 84% and 49%. It is worth noting that, opposing Lure Of Flames, a once summoned elemental can't lose permanent Willpower due to botches and can attemp every turn.
A minor fire elemental rolls 10 dice of aggravated damage in WtA! In VtM it's just 3 dice, even weaker than Lure Of Flames.
As this elemental has Gnosis of 10, he can always get a free marginal success if not in combat, then he has the following chances for at least 1 success against given difficulty: 3-4/99%, 5/98%, 6/95%, 7/89%, 8/79%. 9/62%, 10/35%. For VtM elemental with dicepool of 3 chances are 3/92%, 4/87%, 5/81%, 6/74%, 7/65%, 8/54%, 9/40% and 10/22%.
On average, WtA elemental would heal 4 levels of lethal damage and 2 levels of aggravated. A VtM elemental would heal 1,2/0,6 levels respectively.
The other two elementals, Glass and Electricity, may not be available for most thaumaturges, but let's still list them.
Blast fires a shard worth 7 dice of aggravated damage.
90% to succeed for WtA elemental, 74% for VtM elemental.
Electricity Elemental
Blast deals 7 dice of damage.
Spirits can also move at extremely quick rates, flying 20+Willpower meters per turn.
So, we now have a clear knowledge of what "any special powers it has related to its element" an elemental could have. What goes to the raw power of an elemental (his stats) is not that easy. Some powers of WtA elementals, such as Fire Elemental's Blast, are definitely overpowered, while using plain VtM stats makes them useless. Some, like Water Elemental's heal, are powerful, but limited.
The problem is that WtA clearly operates greater numbers than VtM. I am not familiar with WtA, but Strength and Agility of 4 and Stamina of 3 of typical Brujah neonate, probably enhanced by 1-2 dots of Potence/Celerity, are clearly weaker than the same stats enhanced by +4/+1/+3 of a Garou in Crinos, given that werewolves also deal aggravated damage with their attacks by default, and can use Rage for extra actions, a lot of them. There are many more other powers that I didn't know of yet, but that's already enough for the purposes of an example. So, pretty surely, we shouldn't give WtA-level powers to VtM characters, at least to those controlled by players.
On the other hand, there are (or there have to be!) reasons that make Thaumaturgy a heavily guarded secret of Tremere, and Elemental Mastery is a not so common path. Mastering it to level 5 would require primary path to be of level 5 already, which is a lot of XP already, plus very high Occult and Manipulation required to control an elemental, otherwise it is hard to benefit from that path, and high Willpower (like at least 8 or probably 9-10) to reliably roll the power. This level of vampire strength is somewhat of how a powerful Tremere ancilla could look like. A character who has gone that far probably deserves a powerful tool in his hands.
Let's compare this path to level 5 Obtenebration. It doesn't require primary path to be learned beforehand, and involves no risk of losing permanent Willpower. Each success on the same Manipulation + Occult roll would summon another tentacle with Strength and Dexterity of 5 (plus some bonus dots from very possible Celerity or Potence (which is an in-clan Discipline for Lasombra)). Manipulation 4 and Occult 5, which would be very reasonable for a Tremere or Lasombra ancilla, would summon 2,7 tentacles on average. Surely, tentacles can only hit and grapple, but that's already good. I assume that Elemental Mastery should summon something of at least similar power.
Pages 378-379 of V20 Corebook show a conversion of WtA stats into VtM. I will try to make a similar chart for elemental spirits; if someone finds a more apporproate way to do it, you are more than welcome. I am going to use a form of "Cheat sheet" as described on page 349 of V20 WtA Corebook.
Earth Elemental
A tank with some crowd-control.
Melee attack damage: 4 (bashing)
Attack type: Elemental punches his opponents with hands made of stone. Damage is lethal if it hits the head. He is considered to be using a weapon for the means of blocking/parrying.
Melee rolling to hit or parry: 6
Initiative (in dice): 7
Soak: 6 (+4 if using Armor), bashing damage is ignored, lethal damage is halved, aggravated can be soaked.
Essence: 20
Special abilities:
Air Elemental
A moving and sentient piece of wind.
Melee attack damage: N/A (is immaterial)
Attack type: N/A, but can use offensive special abilities.
Melee rolling to hit: N/A
Initiative (in dice): 3
Soak: 3 (but can only be harmed by supernatural means except for those like Movement of the Mind, which damage through not so supernatural ways)
Essence: 18
Special abilities:
Equivalent of Movement of the Mind 8 (not considered to be a use of magic). Uses 1 point of Essence per throw.
Air Elemental cannot be seen unless observerd with Auspex, only heared or felt.
Fire Elemental
Damage dealer with ability to cause Rötschreck.
Attack damage: N/A
Attack type: N/A
Melee rolling to hit: N/A
Initiative (in dice): 5
Soak: 3 (though it may be hard to find a way to harm a living fire!).
Essence: 20
Special abilities:
Causes Rötschreck. Difficulty to resist is 6 for observing an elemental, 7 if being attacked by him at a distance, 8 if being trapped inside him. A thaumaturge automatically resists it if he controls the elemental.
Equivalent of Lure Of Flames level 5, rolling 7 dice. If elemental is created using green abyssal fire, such as fire summoned by The Fires of the Inferno, elemental will also be made of such a fire and instead have level 5 Fires of the Inferno path (same soak difficulty, but inflicting up to 5 levels of aggravated damage per turn). 1 point of Essence per use.
Can move to a target and trap it inside him, inflicting damage as if the target was fully covered by fire (3 levels of damage per turn, soak difficulty 6). His target may attempt to dodge, a resisted roll will be issued in that case. Elemental rolls 5 dice, and his target rolls Dexterity + Athletics. Each success that elemental scores above his target inflicts one level of damage.
If elemental is standing in fire, it is healed by it instead of being damaged. Fire summoned by himself does count. Instead of being healed, an elemental can regenerate a point of essence.
Those who try to attack elemental in close combat suffer one level of fire damage (soak difficulty 6).
If touching flammabale objects, the elemental may ignite them.
Water Elemental
A healer/support unit.
Melee attack damage: 3 (bashing)
Attack type: A humanlike transparent whater physically hits you right in the face. Gotcha!
Melee rolling to hit: 6
Initiative (in dice): 6
Soak: 7, ignores bashing and lethal.
Essence: 20
Special abilities:
Can spend a point of Essence to raise the natural water level of a place where he stands, possible breaking through stone and asphalt. No roll required. An elemental can flood a whole building or a city block. A spirit can flood a larger area by spending more Essence.
Once per scene per target may heal 10 dice of damage, difficulty is 6 per lethal damage and 8 per aggravated.
Can move to a target and trap it inside him, making it to choke if it needs to breath, inflicting damage as it was standing in fire if it is a Fire Elemental (though Water elemental will get the same damage), and constricting it. His target may attempt to dodge, a resisted roll will be issued in that case. Elemental rolls 5 dice, and his target rolls Dexterity + Athletics. If elemental scores more successes, the target is captured, otherwise it escapes.
If elemental is standing in water, it is healed by it as other creatures get damaged when they stand in fire (3 health levels per turn if it is fully flooded by water, for example). Water summoned by himself does count. Instead of being healed, an elemental can regenerate a point of essence per would-be-healed health level.
While being in a flooded area (possibly by the elemental himself), it is possible to purge spiritual corruption. Elemental rolls 10 dice, but the difficulty depends on corruption Strength.
Glass Elemental
Melee damage dealer.
Melee attack damage: 7 (aggravated)
Attack type: Elemental strikes with his spiky arm made of glass.
Melee rolling to hit: 4
Initiative (in dice): 4
Soak: 4
Essence: 18
Special abilities:
Electricity elemental
Attack damage: 7 (electricity: lethal, but aggravated if soak roll is botched)
Attack type: Zap-zap! An elemental hits you by a lightning.
Melee rolling to hit: No roll required!
Initiative (in dice): 6
Soak: 6
Essence: 18
Special abilities: - Rolling 5 dice, an elemental may control target electrical system or device in his line of sight as if he was standing behind the controls, difficulty is based on the device's complexity and is determined by the Storyteller. It is possible to shut a device down, overload circuits. - Rolling the same 5 dice, a spirit can overload target circuits. It is important, though, that some systems may have built-in protection against overloads, in which case they may soak this damage. Amount of soak dice depends on the protection power.
All elementals may soak aggravated damage. Their Social and Mental abilities range from 5 to 7. They may move with a speed of 20 + Initiative meters per turn.
I am sure that there is a lot to fix and edit right now, but I will look at the answer again in the next couple of days for the sake of fresh perspective.