As a Marauder I only have reliable intelligence and dexterity from the special +30 nodes. So I'm not looking to cast anything at max level, low level should be good enough. I also play hardcore, so no point in suggesting town portal on-death casting.
Normally I don't cast any non-melee spells and don't know anything about them. But it might be good to have some of them. Ideally I'd have two who are good on both kill and damage taken, I only have experience with strength spells.
On damage taken: Molten Shell, Abyssal Cry, Totem (mostly Decoy Totem), Summon (Flame/Stone) Golem (bonuses apply to the player)
On kill: Warlord's Mark, Rallying Cry
After testing more I've found a lot of these spells aren't being cast. I'm not using vaal skills or reserved mana skills or supporting them with anything else. One of the skills is too high level. But Rallying Cry isn't and I can still cast it manually, so clearly it's not being supported by the on damage taken.
Apparently war cries can't be cast through these types of support gems.
And it doesn't work with totems either.
Best Answer
Rallying Cry has the property "Warcry" and is not actually a spell anymore. This means is cannot be cast from trigger spells like Cast on Damage Taken and Cast on Melee Kill. It is manual cast only and also has a global 4 second cooldown.
Totems have their own special "Totem" property as well, and also do not work with "Cast on X" support gems. They are also subject to the totem limit (1 per character by default, with some special exceptions).
Furthermore, Cast on Melee Kill must be linked to both the spell you want to cast on kill and the melee ability you are killing with. It does not create a character-wide effect like Cast on Damage Taken. This means you need at minimum a three-link with the melee skill you want to use to trigger the spells.
And finally, there is an internal cooldown as well as a spell ordering for each "Cast on X" gem your character has. This means you won't ever cast two spells at a time from the same "Cast on X" effect, and they won't cast the same skill twice in a row if there are multiple valid spells linked up. From what I remember mana is never taken into account for these spellcasts though, so they are always free (especially important to know if you take Blood Magic).
Unfortunately, this means you can't easily create a character that summons totems in rapid succession on kill, sustained by Warcrys. Generally, unless you heavily center your build around Cast on Kill, it is better to link the melee skill to something with more damage or better utility.