Use "Double Summon" for an additional 2 Normal Summons as the effect of "Hip Hippo" doesn't count towards the effect of "Double Summon".
This card can be mildly useful in a "Dark Magician" Deck, acting as a backup plan to "Legion the Fiend Jester" and "Double Coston" to Tribute Summon "Dark Magician". The advantage this card has over "Double Coston" is that it grants the ability for an additional Tribute Summon alongside the Normal Summoning of "Hip Hippo", which allows "Dark Magician" to hit the field faster without the use of cards like "Double Summon". While "Legion" is better than "Hip Hippo" for this purpose, "Hip Hippo" can be a useful substitute if "Legion" isn't available.
This card can be useful in a "Kaiju" Deck; its effect would, provided there is another monster already on your field ("Unknown Synchron" is a good option), allow yourself to Tribute Summon a powerful high-Level "Kaiju" without having to Summon one to the opponent's field.