When exactly do I make a saving throw?

I had a slight argument with my DM and another player a few weeks ago when we were playing a modified version of D&D 4th. My wizard(-ish) character attacked another PC with a spell (specifically phantasmal force) while under mind control(sort of) and when I hit him the DM said that the other guy should make a will save. I said that doing so would not make sense because I had already rolled against his Will in the attack roll and succeeded.

They argued that saving throws are made when a PC (but not an NPC) is attacked by a spell and if the save succeeds then the effect is negated. This really does not make sense to me. Now, this very case eventually got resolved without halting the game too much but I would like to know in case the question pops up again.

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having to defeat will and getting a saving throw seems wrong. It provides 2 chances for them to overcome your spell. Did your gm recently move to 4th from a different system? – Colin D May 28 '12 at 15:32
@Colin D He did not recently move to 4th. However, the only source of rules we have is what came in the 4-ed redbox. and we just kind of make the rest up on the spot or borrow rules from 3.5 which we play with another DM. but when this situation popped up we realised that we had never in eighter 4th or 3.5 ever encountered a mage who chucked a spell directly at us. – Circusfreak May 28 '12 at 15:46
A bit tangential, but if you are looking at expanding from just using the red box, rpg.stackexchange.com/questions/1173/…, rpg.stackexchange.com/questions/8225/… and rpg.stackexchange.com/questions/8552/… have some information on doing so – Simon Withers May 28 '12 at 16:57

Unless the effect says to make a saving throw immediately, as when avoiding being pushed into a pit or something, a creature makes saving throws at the end of its turn for each of the effects that a save can end. (Rules Compendium, page 228). In this case, your spell would go into effect on your attack, and at the end of the other PCs turn, he'd get to make a save to shake it off.

(D&D 4e and 3.5 handle saving throws very differently; going back and forth between them could certainly be confusing.)

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As Jadasc said, unless the power explicitly says to make a save immediately or the target has an ability that lets them make a save immediately (hobgoblins and many boss monsters do), or it's a situation that always allows an immediate save (the only one I know of is to fall prone instead of being pushed into something nasty), then you only make saves at the end of your turn. On a side note, in 4e the default mind control status, dominated, only allows the enemy to make you use at-will abilities; 4e isn't designed for PvP, so monsters rarely get to have you go all-out on your allies. – Oblivious Sage May 28 '12 at 17:56
@ObliviousSage It was not really mind control. the DM had invented a quite imaginative scenario in which someone had teleported us and himself into a maze and put a curse on us that would make us see eachother as enemies and force us to attack. At the beginning of each round we could make a roll to resist the curse for that turn.(so, sort of like a save) – Circusfreak May 28 '12 at 18:26
@Circusfreak: You might point out to your DM that monster HP goes up faster than player HP (defenses as well if you're using the Red Box). By level 7 or 8 many players will be able to take another player from full health to unconscious in a single round. – Oblivious Sage May 28 '12 at 18:31
@Circusfreak Understood. The 4e way to handle that would be to have the save at the end of the round to become immune for the rest of the encounter, rather than at the beginning of the round to be immune for the coming turn. If he wants to have you save more often, then perhaps successful psychic or psionic attacks could grant an additional save. – Jadasc May 28 '12 at 18:41
so have I understood it right: I only get to save against spells if it either says I can on the spell or if its an ongoing effect and in the latter case its at the end of the turn? – Circusfreak May 28 '12 at 19:57

As always ... whatever your DM says is how the universe works ...

And it's also worthwhile remembering that 4E has the Rule of Exception as a basic concept, so again having the exception that the PC can roll a Will saving throw is valid, even in standard 4E