You have mentioned gimmick characters before, so just to clarify, your are referring to beings like
Antaios?, who could only be killed as long as no part of his body was in contact with the earth. Just curious.
Also that, but I mainly meant something else.
Usually, with gimmick, most Godly Beings obtain a Deadly Weakness that make them feasable to beat. For example, Odin and Ra have been heavily injured in some Official stories from their mythos, but repeating that probably won't be enough to keep them dead this go-around. So, you'll have to weaken them - with either Thinner, Decodification or Canon Weaknessess - , and only them you can bash their head with a weapon.
Meanwhile, on the other side of the godly spectrum, we have a good chunk of Gods (Celtic, Shinto, Greek, Hindu) that are either too used to death (see the Hindu) , or have no weaknessess (see Greeks). In that case, I have to make up something on the fly, usually making it fit tematichaly with the godly being. For example, if you wanted to kill Demeter, you would have to corner her in an area where No Vegetation Can Flourish, then splash her with Thinner, and THEN you can just kill her.
Honestly, this applies to other "gimmick" being, godly or non: weaken them with known methods, and then try anything that might make sense.
Again, the whole point of "gimmick" is to make things both fair and interesting: if every opponent could be defeated without toughts, then why bother with them? Likewise, if the enemy is Immortal and/or resist anything, Players WILL get tired of them.