Note that this card's effect triggers no matter how it gets to the graveyard; when Milled, or if detached as an Xyz Material, the owner can still activate this card's effect.
If Normal Summoned, you can use "Creature Swap" to take away your opponent's troublesome monsters, such as "Wind-Up Zenmaines" and "Leo" will still destroy itself during the end phase, costing your opponent a monster with no loss to you, plus giving you a free search of any Heraldic Beast from your Deck.
You can use this card to pay the cost of Summoning "Manticore of Darkness", then use its effect to search a Heraldic Beast monster from your Deck, mitigating the cost of "Manticore's" effect.
This card has excellent synergy with either effect of "Heraldic Beast Amphisbaena", which can discard "Leo" to special summon itself or boost its ATK while "Leo's" search effect prevents the user from loosing Card Advantage. Note, however, that "Leo's" effect can only trigger once per turn.