Making d20 Creatures Interesting: Phase Venom
In general, d20 games are more fun if the foes have abilities that require PCs to make interesting decisions.
Ideally these abilities can be easily figured out (perhaps after being experienced a time or two), follow an internal logic, and force the players to try new things without being frustrating or overpowered.
Phase venom. A creature with phase venom is out of phase with all standard planes of existence. It takes only 50% of the damage inflicted on it, and it only 50% likely to be effected by nondamaging effects.
All the creature’s attacks infect targets injured with phase venom, causing them to be more in-phase with it, and less with the normal universe. Such targets do full damage to the phase venom creature and have nondamaging effects affect it, normally, but receive 50% less healing from allies not at the same phase, and each round are 50% less likely in that round to be affected by non-damage based abilities (such as beneficial spells) cast by allies not at the same phase. They also take only 50% damage from creatures not out-of-phase, and are only 50% likely to be affected by such foe’s nondamaging effects.
A target of phase venom becomes fully in-phase with their normal reality after one minute.
Now, this makes a creature very resistant to PC attacks, but it also gives them a way to make it less resistant, at the cost of potentially being more cut off from ally support. OTOH, if the phase venom creature is used in a fight with creatures that don’t have that ability, a PC that becomes out-of-phase is actually harder for some foes to hurt… which may cause them to target in-phase foes.
None of this is overpowering, but it adds a new element to an encounter, forcing PCs to decide who is best to face off against each kind of foe.
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