What spells are good to link to cast on damage taken and melee kill

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.

I recently attempted a 'Retaliation build' and these skills works decently:

Cast on damage taken:

Ice Nova - This slows and slightly damages everything around you after breaking the damage threshold of the On Damage Taken, giving you time to use a potion or leap away from the danger zone. Can also be combined with Knockback Support to give even more room, more for survival than damage dealing.

Ball Lightning - Since the amount of casts you make is dependant on the level of Cast on Damage Taken, persistent spells are more effective than single shot ones at dealing damage. Downside being you are not in absolute control where the ball is headed, unless all your enemies are in the same direction.

Arctic Breath - I didn't use this skill myself but since you have a problem of low int, this is a hybrid skill therefore should be able to be raised to a higher level than the other two. Also the DPS after will further increase it's effectiveness compared to other skills.

That said, since you are using a mostly str Marauder, why not just use Vengeance? It gives a chance to do AOE around yourself when hit. If you instead have a decent shield with high block change you can instead consider Reckoning which hits in a cone on block. Maybe even both.

Cast on Melee Kill:

I didn't put much effort here as unlike Cast on Damage Taken this is less effective on Bosses since you are not constantly killing them.

I did remember seeing this guy using Dominating Blow to trigger Cast on Melee Kill to summon Raging Spirits. Since there is only 1-3 slots left for other support gems on this combo, expect the minions to be weak, however Raging Spirits have a really high limit compared to other minions and them being temporal summon and not targetable by monsters make them a great addition to your overall damage done.

So just put some damage boosting support gems and that'll work. I did not try it out myself but witnessing it is enough to convince me that it is effective. Just make sure you hit enemies with low hp with your Dominating Blow and the rest will work out.